Cleanup and friction reduction
For #65355.
Change-Id: Ia14c9dc584a529a35b97801dd3e95b9acc99a511
Reviewed-on: https://go-review.googlesource.com/c/go/+/600436
Reviewed-by: Keith Randall <khr@google.com>
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callbackUpdateSystemStack contains a fast path to exit early without
update if SP is already within the g0.stack bounds.
This is not safe, as a subsequent call may have new stack bounds that
only partially overlap the old stack bounds. In this case it is possible
to see an SP that is in the old stack bounds, but very close to the
bottom of the bounds due to the partial overlap. In that case we're very
likely to "run out" of space on the system stack.
We only need to do this on extra Ms, as normal Ms have precise bounds
defined when we allocated the stack.
TSAN annotations are added to x_cgo_getstackbounds because bounds is a
pointer into the Go stack. The stack can be reused when an old thread
exits and a new thread starts, but TSAN can't see the synchronization
there. This isn't a new case, but we are now calling more often.
Fixes#62440.
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Change-Id: I5389050494987b7668d0b317fb92f85e61d798ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/584597
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Currently the runtime only tracks the PC and SP upon entering a syscall,
but not the FP (BP). This is mainly for historical reasons, and because
the tracer (which uses the frame pointer unwinder) does not need it.
Until it did, of course, in CL 567076, where the tracer tries to take a
stack trace of a goroutine that's in a syscall from afar. It tries to
use gp.sched.bp and lots of things go wrong. It *really* should be using
the equivalent of gp.syscallbp, which doesn't exist before this CL.
This change introduces gp.syscallbp and tracks it. It also introduces
getcallerfp which is nice for simplifying some code. Because we now have
gp.syscallbp, we can also delete the frame skip count computation in
traceLocker.GoSysCall, because it's now the same regardless of whether
frame pointer unwinding is used.
Fixes#66889.
Change-Id: Ib6d761c9566055e0a037134138cb0f81be73ecf7
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-nocgo
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This change removes the allocheaders, deleting all the old code and
merging mbitmap_allocheaders.go back into mbitmap.go.
This change also deletes the SetType benchmarks which were already
broken in the new GOEXPERIMENT (it's harder to set up than before). We
weren't really watching these benchmarks at all, and they don't provide
additional test coverage.
Change-Id: I135497201c3259087c5cd3722ed3fbe24791d25d
Reviewed-on: https://go-review.googlesource.com/c/go/+/567200
Reviewed-by: Keith Randall <khr@google.com>
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Windows syscall.SyscallN currently calls lockOSThread for every syscall.
This can be expensive and produce unnecessary context switches,
especially when the syscall is called frequently under high contention.
The lockOSThread was necessary to ensure that cgocall wouldn't
reschedule the goroutine to a different M, as the syscall return values
are reported back in the M struct.
This CL instructs cgocall to copy the syscall return values into the
the M that will see the caller on return, so the caller no longer needs
to call lockOSThread.
Updates #58336.
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Change-Id: If6644fd111dbacab74e7dcee2afa18ca146735da
Reviewed-on: https://go-review.googlesource.com/c/go/+/562915
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
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This change replaces the 1-bit-per-word heap bitmap for most size
classes with allocation headers for objects that contain pointers. The
header consists of a single pointer to a type. All allocations with
headers are treated as implicitly containing one or more instances of
the type in the header.
As the name implies, headers are usually stored as the first word of an
object. There are two additional exceptions to where headers are stored
and how they're used.
Objects smaller than 512 bytes do not have headers. Instead, a heap
bitmap is reserved at the end of spans for objects of this size. A full
word of overhead is too much for these small objects. The bitmap is of
the same format of the old bitmap, minus the noMorePtrs bits which are
unnecessary. All the objects <512 bytes have a bitmap less than a
pointer-word in size, and that was the granularity at which noMorePtrs
could stop scanning early anyway.
Objects that are larger than 32 KiB (which have their own span) have
their headers stored directly in the span, to allow power-of-two-sized
allocations to not spill over into an extra page.
The full implementation is behind GOEXPERIMENT=allocheaders.
The purpose of this change is performance. First and foremost, with
headers we no longer have to unroll pointer/scalar data at allocation
time for most size classes. Small size classes still need some
unrolling, but their bitmaps are small so we can optimize that case
fairly well. Larger objects effectively have their pointer/scalar data
unrolled on-demand from type data, which is much more compactly
represented and results in less TLB pressure. Furthermore, since the
headers are usually right next to the object and where we're about to
start scanning, we get an additional temporal locality benefit in the
data cache when looking up type metadata. The pointer/scalar data is
now effectively unrolled on-demand, but it's also simpler to unroll than
before; that unrolled data is never written anywhere, and for arrays we
get the benefit of retreading the same data per element, as opposed to
looking it up from scratch for each pointer-word of bitmap. Lastly,
because we no longer have a heap bitmap that spans the entire heap,
there's a flat 1.5% memory use reduction. This is balanced slightly by
some objects possibly being bumped up a size class, but most objects are
not tightly optimized to size class sizes so there's some memory to
spare, making the header basically free in those cases.
See the follow-up CL which turns on this experiment by default for
benchmark results. (CL 538217.)
Change-Id: I4c9034ee200650d06d8bdecd579d5f7c1bbf1fc5
Reviewed-on: https://go-review.googlesource.com/c/go/+/437955
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Reviewed-by: Keith Randall <khr@golang.org>
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With the introduction of runtime.Pinner, returning a pointer to a pinned
struct that then points to an unpinned Go pointer is correctly caught.
However, the error message remained as "cgo result has Go pointer",
which should be updated to acknowledge that Go pointers to pinned
memory are allowed.
This also updates the comments for cgoCheckArg and cgoCheckResult
to similarly clarify.
Updates #46787
Change-Id: I147bb09e87dfb70a24d6d43e4cf84e8bcc2aff48
GitHub-Last-Rev: 706facb9f2
GitHub-Pull-Request: golang/go#62606
Reviewed-on: https://go-review.googlesource.com/c/go/+/527702
Reviewed-by: Michael Knyszek <mknyszek@google.com>
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For cgo callbacks, currently cgocallbackg locks the OS thread and
then call cgocallbackg1, which invokes the actual callback, and
then unlocks the OS thread in a deferred call. cgocallback then
continues assuming we are on the same M. This assumes there is no
preemption point between the deferred unlockOSThread and returning
to the caller (cgocallbackg). But this is not always true. E.g.
when open defer is not used (e.g. PIE or shared build mode on 386),
there is a preemption point in deferreturn after invoking the
deferred function (when it checks whether there are still defers
to run).
Instead of relying on and requiring the defer implementation has
no preemption point, we move the unlockOSThread to the caller, and
ensuring no preemption by setting incgo to true before unlocking.
This doesn't cover the panicking path, so we also adds an
unlockOSThread there. There we don't need to worry about preemption,
because we're panicking out of the callback and we have unwound the
g0 stack, instead of reentering cgo.
Fixes#62102.
Change-Id: I0e0b9f9091be88d01675c0acb7339b81402545be
Reviewed-on: https://go-review.googlesource.com/c/go/+/532615
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[This is an unmodified redo of CL 527056.]
Standard Ms set g0.stackguard1 to the same value as stackguard0 in
mstart0. For consistency, extra Ms should do the same for their g0. Do
this in needm -> callbackUpdateSystemStack.
Background: getg().stackguard1 is used as the stack guard for the stack
growth prolouge in functions marked //go:systemstack [1]. User Gs set
stackguard1 to ^uintptr(0) so that the check always fail, calling
morestackc, which throws to report a //go:systemstack function call on a
user stack.
g0 setting stackguard1 is unnecessary for this functionality. 0 would be
sufficient, as g0 is always allowed to call //go:systemstack functions.
However, since we have the check anyway, setting stackguard1 to the
actual stack bound is useful to detect actual stack overflows on g0
(though morestackc doesn't detect this case and would report a
misleading message about user stacks).
[1] cmd/internal/obj calls //go:systemstack functions AttrCFunc. This is
a holdover from when the runtime contained actual C functions. But since
CL 2275, it has simply meant "pretend this is a C function, which would
thus need to use the system stack". Hence the name morestackc. At this
point, this terminology is pretty far removed from reality and should
probably be updated to something more intuitive.
Change-Id: If315677217354465fbbfbd0d406d79be20db0cc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/527716
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[This is a redo of CL 525455 with the test fixed on darwin by defining
_XOPEN_SOURCE, and disabled with android, musl, and openbsd, which do
not provide getcontext.]
Since CL 495855, Ms are cached for C threads calling into Go, including
the stack bounds of the system stack.
Some C libraries (e.g., coroutine libraries) do manual stack management
and may change stacks between calls to Go on the same thread.
Changing the stack if there is more Go up the stack would be
problematic. But if the calls are completely independent there is no
particular reason for Go to care about the changing stack boundary.
Thus, this CL allows the stack bounds to change in such cases. The
primary downside here (besides additional complexity) is that normal
systems that do not manipulate the stack may not notice unintentional
stack corruption as quickly as before.
Note that callbackUpdateSystemStack is written to be usable for the
initial setup in needm as well as updating the stack in cgocallbackg.
Fixes#62440.
For #62130.
Change-Id: I0fe0134f865932bbaff1fc0da377c35c013bd768
Reviewed-on: https://go-review.googlesource.com/c/go/+/527715
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This reverts CL 525455. The test fails to build on darwin, alpine, and
android.
For #62440.
Change-Id: I39c6b1e16499bd61e0f166de6c6efe7a07961e62
Reviewed-on: https://go-review.googlesource.com/c/go/+/527317
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This reverts CL 527056.
CL 525455 breaks darwin, alpine, and android. This CL must be reverted
in order to revert that CL.
For #62440.
Change-Id: I4e1b16e384b475a605e0214ca36c918d50faa22c
Reviewed-on: https://go-review.googlesource.com/c/go/+/527316
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Standard Ms set g0.stackguard1 to the same value as stackguard0 in
mstart0. For consistency, extra Ms should do the same for their g0. Do
this in needm -> callbackUpdateSystemStack.
Background: getg().stackguard1 is used as the stack guard for the stack
growth prolouge in functions marked //go:systemstack [1]. User Gs set
stackguard1 to ^uintptr(0) so that the check always fail, calling
morestackc, which throws to report a //go:systemstack function call on a
user stack.
g0 setting stackguard1 is unnecessary for this functionality. 0 would be
sufficient, as g0 is always allowed to call //go:systemstack functions.
However, since we have the check anyway, setting stackguard1 to the
actual stack bound is useful to detect actual stack overflows on g0
(though morestackc doesn't detect this case and would report a
misleading message about user stacks).
[1] cmd/internal/obj calls //go:systemstack functions AttrCFunc. This is
a holdover from when the runtime contained actual C functions. But since
CL 2275, it has simply meant "pretend this is a C function, which would
thus need to use the system stack". Hence the name morestackc. At this
point, this terminology is pretty far removed from reality and should
probably be updated to something more intuitive.
Change-Id: I8d0e5628ce31ac6a189a7d7a4124be85aef89862
Reviewed-on: https://go-review.googlesource.com/c/go/+/527056
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Since CL 495855, Ms are cached for C threads calling into Go, including
the stack bounds of the system stack.
Some C libraries (e.g., coroutine libraries) do manual stack management
and may change stacks between calls to Go on the same thread.
Changing the stack if there is more Go up the stack would be
problematic. But if the calls are completely independent there is no
particular reason for Go to care about the changing stack boundary.
Thus, this CL allows the stack bounds to change in such cases. The
primary downside here (besides additional complexity) is that normal
systems that do not manipulate the stack may not notice unintentional
stack corruption as quickly as before.
Note that callbackUpdateSystemStack is written to be usable for the
initial setup in needm as well as updating the stack in cgocallbackg.
Fixes#62440.
For #62130.
Change-Id: I7841b056acea1111bdae3b718345a3bd3961b4a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/525455
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When passing pointers of Go objects from Go to C, the cgo command generate _Cgo_use(pN) for the unsafe.Pointer type arguments, so that the Go compiler will escape these object to heap.
Since the C function may callback to Go, then the Go stack might grow/shrink, that means the pointers that the C function have will be invalid.
After adding the #cgo noescape annotation for a C function, the cgo command won't generate _Cgo_use(pN), and the Go compiler won't force the object escape to heap.
After adding the #cgo nocallback annotation for a C function, which means the C function won't callback to Go, if it do callback to Go, the Go process will crash.
Fixes#56378
Change-Id: Ifdca070584e0d349c7b12276270e50089e481f7a
GitHub-Last-Rev: f1a17b08b0
GitHub-Pull-Request: golang/go#60399
Reviewed-on: https://go-review.googlesource.com/c/go/+/497837
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Some C APIs require the use or structures that contain pointers to
buffers (iovec, io_uring, ...). The pointer passing rules would
require that these buffers are allocated in C memory and to process
this data with Go libraries it would need to be copied.
In order to provide a zero-copy way to use these C APIs, this CL
implements a Pinner API that allows to pin Go objects, which
guarantees that the garbage collector does not move these objects
while pinned. This allows to relax the pointer passing rules so that
pinned pointers can be stored in C allocated memory or can be
contained in Go memory that is passed to C functions.
The Pin() method accepts pointers to objects of any type and
unsafe.Pointer. Slices and arrays can be pinned by calling Pin()
with the pointer to the first element. Pinning of maps is not
supported.
If the GC collects unreachable Pinner holding pinned objects it
panics. If Pin() is called with the other non-pointer types it
panics as well.
Performance considerations: This change has no impact on execution
time on existing code, because checks are only done in code paths,
that would panic otherwise. The memory footprint on existing code is
one pointer per memory span.
Fixes: #46787
Signed-off-by: Sven Anderson <sven@anderson.de>
Change-Id: I110031fe789b92277ae45a9455624687bd1c54f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/367296
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This reapplies CL 485500, with a fix drafted in CL 492987 incorporated.
CL 485500 is reverted due to #60004 and #60007. #60004 is fixed in
CL 492743. #60007 is fixed in CL 492987 (incorporated in this CL).
[Original CL 485500 description]
This reapplies CL 481061, with the followup fixes in CL 482975, CL 485315, and
CL 485316 incorporated.
CL 481061, by doujiang24 <doujiang24@gmail.com>, speed up C to Go
calls by binding the M to the C thread. See below for its
description.
CL 482975 is a followup fix to a C declaration in testprogcgo.
CL 485315 is a followup fix for x_cgo_getstackbound on Illumos.
CL 485316 is a followup cleanup for ppc64 assembly.
CL 479915 passed the G to _cgo_getstackbound for direct updates to
gp.stack.lo. A G can be reused on a new thread after the previous thread
exited. This could trigger the C TSAN race detector because it couldn't
see the synchronization in Go (lockextra) preventing the same G from
being used on multiple threads at the same time.
We work around this by passing the address of a stack variable to
_cgo_getstackbound rather than the G. The stack is generally unique per
thread, so TSAN won't see the same address from multiple threads. Even
if stacks are reused across threads by pthread, C TSAN should see the
synchonization in the stack allocator.
A regression test is added to misc/cgo/testsanitizer.
[Original CL 481061 description]
This reapplies CL 392854, with the followup fixes in CL 479255,
CL 479915, and CL 481057 incorporated.
CL 392854, by doujiang24 <doujiang24@gmail.com>, speed up C to Go
calls by binding the M to the C thread. See below for its
description.
CL 479255 is a followup fix for a small bug in ARM assembly code.
CL 479915 is another followup fix to address C to Go calls after
the C code uses some stack, but that CL is also buggy.
CL 481057, by Michael Knyszek, is a followup fix for a memory leak
bug of CL 479915.
[Original CL 392854 description]
In a C thread, it's necessary to acquire an extra M by using needm while invoking a Go function from C. But, needm and dropm are heavy costs due to the signal-related syscalls.
So, we change to not dropm while returning back to C, which means binding the extra M to the C thread until it exits, to avoid needm and dropm on each C to Go call.
Instead, we only dropm while the C thread exits, so the extra M won't leak.
When invoking a Go function from C:
Allocate a pthread variable using pthread_key_create, only once per shared object, and register a thread-exit-time destructor.
And store the g0 of the current m into the thread-specified value of the pthread key, only once per C thread, so that the destructor will put the extra M back onto the extra M list while the C thread exits.
When returning back to C:
Skip dropm in cgocallback, when the pthread variable has been created, so that the extra M will be reused the next time invoke a Go function from C.
This is purely a performance optimization. The old version, in which needm & dropm happen on each cgo call, is still correct too, and we have to keep the old version on systems with cgo but without pthreads, like Windows.
This optimization is significant, and the specific value depends on the OS system and CPU, but in general, it can be considered as 10x faster, for a simple Go function call from a C thread.
For the newly added BenchmarkCGoInCThread, some benchmark results:
1. it's 28x faster, from 3395 ns/op to 121 ns/op, in darwin OS & Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
2. it's 6.5x faster, from 1495 ns/op to 230 ns/op, in Linux OS & Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
[CL 479915 description]
Currently, when C calls into Go the first time, we grab an M
using needm, which sets m.g0's stack bounds using the SP. We don't
know how big the stack is, so we simply assume 32K. Previously,
when the Go function returns to C, we drop the M, and the next
time C calls into Go, we put a new stack bound on the g0 based on
the current SP. After CL 392854, we don't drop the M, and the next
time C calls into Go, we reuse the same g0, without recomputing
the stack bounds. If the C code uses quite a bit of stack space
before calling into Go, the SP may be well below the 32K stack
bound we assumed, so the runtime thinks the g0 stack overflows.
This CL makes needm get a more accurate stack bound from
pthread. (In some platforms this may still be a guess as we don't
know exactly where we are in the C stack), but it is probably
better than simply assuming 32K.
[CL 492987 description]
On the first call into Go from a C thread, currently we set the g0
stack's high bound imprecisely based on the SP. With CL 485500, we
keep the M and don't recompute the stack bounds when it calls into
Go again. If the first call is made when the C thread uses some
deep stack, but a subsequent call is made with a shallower stack,
the SP may be above g0.stack.hi.
This is usually okay as we don't check usually stack.hi. One place
where we do check for stack.hi is in the signal handler, in
adjustSignalStack. In particular, C TSAN delivers signals on the
g0 stack (instead of the usual signal stack). If the SP is above
g0.stack.hi, we don't see it is on the g0 stack, and throws.
This CL makes it get an accurate stack upper bound with the
pthread API (on the platforms where it is available).
Also add some debug print for the "handler not on signal stack"
throw.
Fixes#51676.
Fixes#59294.
Fixes#59678.
Fixes#60007.
Change-Id: Ie51c8e81ade34ec81d69fd7bce1fe0039a470776
Reviewed-on: https://go-review.googlesource.com/c/go/+/495855
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This refactoring is more problematic because the client
package wrap abi.Type, thus the self-referential fields
within ArrayType need to be downcast to the client wrappers
in several places. It's not clear to me this is worthwhile;
this CL is for additional comment, before I attempt similar
changes for other self-referential types.
Change-Id: I41e517e6d851b32560c41676b91b76d7eb17c951
Reviewed-on: https://go-review.googlesource.com/c/go/+/466236
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This touches a lot of files, which is bad, but it is also good,
since there's N copies of this information commoned into 1.
The new files in internal/abi are copied from the end of the stack;
ultimately this will all end up being used.
Change-Id: Ia252c0055aaa72ca569411ef9f9e96e3d610889e
Reviewed-on: https://go-review.googlesource.com/c/go/+/462995
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This reverts CL 485500.
Reason for revert: This breaks internal tests at Google, see b/280861579 and b/280820455.
Change-Id: I426278d400f7611170918fc07c524cb059b9cc55
Reviewed-on: https://go-review.googlesource.com/c/go/+/492995
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Run-TryBot: Chressie Himpel <chressie@google.com>
The current mp.incgocallback() logic allows for trace events to be
recorded using frame pointer unwinding during cgocallbackg when they
shouldn't be. Specifically, mp.incgo will be false during the
reentersyscall call at the end. It's possible to crash with tracing
enabled because of this, if C code which uses the frame pointer register
for other purposes calls into Go. This can be seen, for example, by
forcing testprogcgo/trace_unix.c to write a garbage value to RBP prior
to calling into Go.
We can drop the mp.incgo check, and instead conservatively avoid doing
frame pointer unwinding if there is any C on the stack. This is the case
if mp.ncgo > 0, or if mp.isextra is true (meaning we're coming from a
thread created by C). Rename incgocallback to reflect that we're
checking if there's any C on the stack. We can also move the ncgo
increment in cgocall closer to where the transition to C happens, which
lets us use frame pointer unwinding for the entersyscall event during
the first Go-to-C call on a stack, when there isn't yet any C on the
stack.
Fixes#59830.
Change-Id: If178a705a9d38d0d2fb19589a9e669cd982d32cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/488755
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Nick Ripley <nick.ripley@datadoghq.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This reapplies CL 481061, with the followup fixes in CL 482975, CL 485315, and
CL 485316 incorporated.
CL 481061, by doujiang24 <doujiang24@gmail.com>, speed up C to Go
calls by binding the M to the C thread. See below for its
description.
CL 482975 is a followup fix to a C declaration in testprogcgo.
CL 485315 is a followup fix for x_cgo_getstackbound on Illumos.
CL 485316 is a followup cleanup for ppc64 assembly.
[Original CL 481061 description]
This reapplies CL 392854, with the followup fixes in CL 479255,
CL 479915, and CL 481057 incorporated.
CL 392854, by doujiang24 <doujiang24@gmail.com>, speed up C to Go
calls by binding the M to the C thread. See below for its
description.
CL 479255 is a followup fix for a small bug in ARM assembly code.
CL 479915 is another followup fix to address C to Go calls after
the C code uses some stack, but that CL is also buggy.
CL 481057, by Michael Knyszek, is a followup fix for a memory leak
bug of CL 479915.
[Original CL 392854 description]
In a C thread, it's necessary to acquire an extra M by using needm while invoking a Go function from C. But, needm and dropm are heavy costs due to the signal-related syscalls.
So, we change to not dropm while returning back to C, which means binding the extra M to the C thread until it exits, to avoid needm and dropm on each C to Go call.
Instead, we only dropm while the C thread exits, so the extra M won't leak.
When invoking a Go function from C:
Allocate a pthread variable using pthread_key_create, only once per shared object, and register a thread-exit-time destructor.
And store the g0 of the current m into the thread-specified value of the pthread key, only once per C thread, so that the destructor will put the extra M back onto the extra M list while the C thread exits.
When returning back to C:
Skip dropm in cgocallback, when the pthread variable has been created, so that the extra M will be reused the next time invoke a Go function from C.
This is purely a performance optimization. The old version, in which needm & dropm happen on each cgo call, is still correct too, and we have to keep the old version on systems with cgo but without pthreads, like Windows.
This optimization is significant, and the specific value depends on the OS system and CPU, but in general, it can be considered as 10x faster, for a simple Go function call from a C thread.
For the newly added BenchmarkCGoInCThread, some benchmark results:
1. it's 28x faster, from 3395 ns/op to 121 ns/op, in darwin OS & Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
2. it's 6.5x faster, from 1495 ns/op to 230 ns/op, in Linux OS & Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
[CL 479915 description]
Currently, when C calls into Go the first time, we grab an M
using needm, which sets m.g0's stack bounds using the SP. We don't
know how big the stack is, so we simply assume 32K. Previously,
when the Go function returns to C, we drop the M, and the next
time C calls into Go, we put a new stack bound on the g0 based on
the current SP. After CL 392854, we don't drop the M, and the next
time C calls into Go, we reuse the same g0, without recomputing
the stack bounds. If the C code uses quite a bit of stack space
before calling into Go, the SP may be well below the 32K stack
bound we assumed, so the runtime thinks the g0 stack overflows.
This CL makes needm get a more accurate stack bound from
pthread. (In some platforms this may still be a guess as we don't
know exactly where we are in the C stack), but it is probably
better than simply assuming 32K.
[CL 485500 description]
CL 479915 passed the G to _cgo_getstackbound for direct updates to
gp.stack.lo. A G can be reused on a new thread after the previous thread
exited. This could trigger the C TSAN race detector because it couldn't
see the synchronization in Go (lockextra) preventing the same G from
being used on multiple threads at the same time.
We work around this by passing the address of a stack variable to
_cgo_getstackbound rather than the G. The stack is generally unique per
thread, so TSAN won't see the same address from multiple threads. Even
if stacks are reused across threads by pthread, C TSAN should see the
synchonization in the stack allocator.
A regression test is added to misc/cgo/testsanitizer.
Fixes#51676.
Fixes#59294.
Fixes#59678.
Change-Id: Ic62be31a06ee83568215e875a891df37084e08ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/485500
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
This reverts CL 481061.
Reason for revert: When built with C TSAN, x_cgo_getstackbound triggers
race detection on `g->stacklo` because the synchronization is in Go,
which isn't instrumented.
For #51676.
For #59294.
For #59678.
Change-Id: I38afcda9fcffd6537582a39a5214bc23dc147d47
Reviewed-on: https://go-review.googlesource.com/c/go/+/485275
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
This reapplies CL 392854, with the followup fixes in CL 479255,
CL 479915, and CL 481057 incorporated.
CL 392854, by doujiang24 <doujiang24@gmail.com>, speed up C to Go
calls by binding the M to the C thread. See below for its
description.
CL 479255 is a followup fix for a small bug in ARM assembly code.
CL 479915 is another followup fix to address C to Go calls after
the C code uses some stack, but that CL is also buggy.
CL 481057, by Michael Knyszek, is a followup fix for a memory leak
bug of CL 479915.
[Original CL 392854 description]
In a C thread, it's necessary to acquire an extra M by using needm while invoking a Go function from C. But, needm and dropm are heavy costs due to the signal-related syscalls.
So, we change to not dropm while returning back to C, which means binding the extra M to the C thread until it exits, to avoid needm and dropm on each C to Go call.
Instead, we only dropm while the C thread exits, so the extra M won't leak.
When invoking a Go function from C:
Allocate a pthread variable using pthread_key_create, only once per shared object, and register a thread-exit-time destructor.
And store the g0 of the current m into the thread-specified value of the pthread key, only once per C thread, so that the destructor will put the extra M back onto the extra M list while the C thread exits.
When returning back to C:
Skip dropm in cgocallback, when the pthread variable has been created, so that the extra M will be reused the next time invoke a Go function from C.
This is purely a performance optimization. The old version, in which needm & dropm happen on each cgo call, is still correct too, and we have to keep the old version on systems with cgo but without pthreads, like Windows.
This optimization is significant, and the specific value depends on the OS system and CPU, but in general, it can be considered as 10x faster, for a simple Go function call from a C thread.
For the newly added BenchmarkCGoInCThread, some benchmark results:
1. it's 28x faster, from 3395 ns/op to 121 ns/op, in darwin OS & Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
2. it's 6.5x faster, from 1495 ns/op to 230 ns/op, in Linux OS & Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
[CL 479915 description]
Currently, when C calls into Go the first time, we grab an M
using needm, which sets m.g0's stack bounds using the SP. We don't
know how big the stack is, so we simply assume 32K. Previously,
when the Go function returns to C, we drop the M, and the next
time C calls into Go, we put a new stack bound on the g0 based on
the current SP. After CL 392854, we don't drop the M, and the next
time C calls into Go, we reuse the same g0, without recomputing
the stack bounds. If the C code uses quite a bit of stack space
before calling into Go, the SP may be well below the 32K stack
bound we assumed, so the runtime thinks the g0 stack overflows.
This CL makes needm get a more accurate stack bound from
pthread. (In some platforms this may still be a guess as we don't
know exactly where we are in the C stack), but it is probably
better than simply assuming 32K.
Fixes#51676.
Fixes#59294.
Change-Id: I9bf1400106d5c08ce621d2ed1df3a2d9e3f55494
Reviewed-on: https://go-review.googlesource.com/c/go/+/481061
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: DeJiang Zhu (doujiang) <doujiang24@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This reverts CL 392854.
Reason for revert: caused #59294, which was derived from google
internal tests. The attempted fix of #59294 caused more breakage.
Change-Id: I5a061561ac2740856b7ecc09725ac28bd30f8bba
Reviewed-on: https://go-review.googlesource.com/c/go/+/481060
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
In a C thread, it's necessary to acquire an extra M by using needm while invoking a Go function from C. But, needm and dropm are heavy costs due to the signal-related syscalls.
So, we change to not dropm while returning back to C, which means binding the extra M to the C thread until it exits, to avoid needm and dropm on each C to Go call.
Instead, we only dropm while the C thread exits, so the extra M won't leak.
When invoking a Go function from C:
Allocate a pthread variable using pthread_key_create, only once per shared object, and register a thread-exit-time destructor.
And store the g0 of the current m into the thread-specified value of the pthread key, only once per C thread, so that the destructor will put the extra M back onto the extra M list while the C thread exits.
When returning back to C:
Skip dropm in cgocallback, when the pthread variable has been created, so that the extra M will be reused the next time invoke a Go function from C.
This is purely a performance optimization. The old version, in which needm & dropm happen on each cgo call, is still correct too, and we have to keep the old version on systems with cgo but without pthreads, like Windows.
This optimization is significant, and the specific value depends on the OS system and CPU, but in general, it can be considered as 10x faster, for a simple Go function call from a C thread.
For the newly added BenchmarkCGoInCThread, some benchmark results:
1. it's 28x faster, from 3395 ns/op to 121 ns/op, in darwin OS & Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
2. it's 6.5x faster, from 1495 ns/op to 230 ns/op, in Linux OS & Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
Fixes#51676
Change-Id: I380702fe2f9b6b401b2d6f04b0aba990f4b9ee6c
GitHub-Last-Rev: 93dc64ad98
GitHub-Pull-Request: golang/go#51679
Reviewed-on: https://go-review.googlesource.com/c/go/+/392854
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: thepudds <thepudds1460@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Move this knob from a binary-startup thing to a build-time thing.
This will enable followon optmizations to the write barrier.
Change-Id: Ic3323348621c76a7dc390c09ff55016b19c43018
Reviewed-on: https://go-review.googlesource.com/c/go/+/447778
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Change-Id: I69065f8adf101fdb28682c55997f503013a50e29
Reviewed-on: https://go-review.googlesource.com/c/go/+/449757
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Joedian Reid <joedian@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joedian Reid <joedian@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
[this is a retry of CL 407035 + its revert CL 422395. The content is unchanged]
Use just 1 bit per word to record the ptr/nonptr bitmap.
Use word-sized operations to manipulate the bitmap, so we can operate
on up to 64 ptr/nonptr bits at a time.
Use a separate bitmap, one bit per word of the ptr/nonptr bitmap,
to encode a no-more-pointers signal. Since we can check 64 ptr/nonptr
bits at once, knowing the exact last pointer location is not necessary.
As a followon CL, we should make the gcdata bitmap an array of
uintptr instead of an array of byte, so we can load 64 bits of it at once.
Similarly for the processing of gc programs.
Change-Id: Ica5eb622f5b87e647be64f471d67b02732ef8be6
Reviewed-on: https://go-review.googlesource.com/c/go/+/422634
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
This reverts commit b589208c8c.
Reason for revert: Bug somewhere in this code, causing wasm and maybe linux/386 to fail.
Change-Id: I5e1e501d839584e0219271bb937e94348f83c11f
Reviewed-on: https://go-review.googlesource.com/c/go/+/422395
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Use just 1 bit per word to record the ptr/nonptr bitmap.
Use word-sized operations to manipulate the bitmap, so we can operate
on up to 64 ptr/nonptr bits at a time.
Use a separate bitmap, one bit per word of the ptr/nonptr bitmap,
to encode a no-more-pointers signal. Since we can check 64 ptr/nonptr
bits at once, knowing the exact last pointer location is not necessary.
This cleans up the bitmap implementation significantly, which will
hopefully make it faster. TODO: measure
As a followon CL, we should make the gcdata bitmap an array of
uintptr instead of an array of byte, so we can load 64 bits of it at once.
Similarly for the processing of gc programs.
Change-Id: I18151b1876d9543599800dec51e2a1b19df97d49
Reviewed-on: https://go-review.googlesource.com/c/go/+/407035
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Previously we stole a bit from the field offset to encode whether
a struct field was embedded.
Instead, encode that bit in the name field, where we already have
some unused bits to play with. The bit associates naturally with
the name in any case.
This leaves a full uintptr to specify field offsets. This will make
the fix for #52740 cleaner.
Change-Id: I0bfb85564dc26e8c18101bc8b432f332176d7836
Reviewed-on: https://go-review.googlesource.com/c/go/+/412138
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
A future change to gofmt will rewrite
// Doc comment.
//go:foo
to
// Doc comment.
//
//go:foo
Apply that change preemptively to all comments (not necessarily just doc comments).
For #51082.
Change-Id: Iffe0285418d1e79d34526af3520b415a12203ca9
Reviewed-on: https://go-review.googlesource.com/c/go/+/384260
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
And then revert the bootstrap cmd directories and certain testdata.
And adjust tests as needed.
Not reverting the changes in std that are bootstrapped,
because some of those changes would appear in API docs,
and we want to use any consistently.
Instead, rewrite 'any' to 'interface{}' in cmd/dist for those directories
when preparing the bootstrap copy.
A few files changed as a result of running gofmt -w
not because of interface{} -> any but because they
hadn't been updated for the new //go:build lines.
Fixes#49884.
Change-Id: Ie8045cba995f65bd79c694ec77a1b3d1fe01bb09
Reviewed-on: https://go-review.googlesource.com/c/go/+/368254
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Using setitimer on Linux to request SIGPROF signal deliveries in
proportion to the process's on-CPU time results in under-reporting when
the program uses several goroutines in parallel. Linux calculates the
process's total CPU spend on a regular basis (often every 4ms); if the
process has spent enough CPU time since the last calculation to warrant
more than one SIGPROF (usually 10ms for the default sample rate of 100
Hz), the kernel is often able to deliver only one of them. With these
common settings, that results in Go CPU profiles being attenuated for
programs that use more than 2.5 goroutines in parallel.
To avoid in effect overflowing the kernel's process-wide CPU counter,
and relying on Linux's typical behavior of having the active thread
handle the resulting process-targeted signal, use timer_create to
request a timer for each OS thread that the Go runtime manages. Have
each timer track the CPU time of a single thread, with the resulting
SIGPROF going directly to that thread.
To continue tracking CPU time spent on threads that don't interact with
the Go runtime (such as those created and used in cgo), keep using
setitimer in addition to the new mechanism. When a SIGPROF signal
arrives, check whether it's due to setitimer or timer_create and filter
as appropriate: If the thread is known to Go (has an M) and has a
timer_create timer, ignore SIGPROF signals from setitimer. If the thread
is not known to Go (does not have an M), ignore SIGPROF signals that are
not from setitimer.
Counteract the new bias that per-thread profiling adds against
short-lived threads (or those that are only active on occasion for a
short time, such as garbage collection workers on mostly-idle systems)
by configuring the timers' initial trigger to be from a uniform random
distribution between "immediate trigger" and the full requested sample
period.
Updates #35057
Change-Id: Iab753c4e5101bdc09ef9132eec84a75478e05579
Reviewed-on: https://go-review.googlesource.com/c/go/+/324129
Run-TryBot: Rhys Hiltner <rhys@justin.tv>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: David Chase <drchase@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Conflicts:
- src/go/types/check_test.go
CL 324730 on dev.typeparams changed the directory paths in TestCheck,
TestExamples, and TestFixedbugs and renamed checkFiles to testFiles;
whereas CL 337529 on master added a new test case just above them and
that used checkFiles.
Merge List:
+ 2021-08-12 46fd547d89 internal/goversion: update Version to 1.18
+ 2021-08-12 5805efc78e doc/go1.17: remove draft notice
+ 2021-08-12 39634e7dae CONTRIBUTORS: update for the Go 1.17 release
+ 2021-08-12 095bb790e1 os/exec: re-enable LookPathTest/16
+ 2021-08-11 dea23e9ca8 src/make.*: make --no-clean flag a no-op that prints a warning
+ 2021-08-11 d4c0ed26ac doc/go1.17: linker passes -I to extld as -Wl,--dynamic-linker
+ 2021-08-10 1f9c9d8530 doc: use "high address/low address" instead of "top/bottom"
+ 2021-08-09 f1dce319ff cmd/go: with -mod=vendor, don't panic if there are duplicate requirements
+ 2021-08-09 7aeaad5c86 runtime/cgo: when using msan explicitly unpoison cgoCallers
+ 2021-08-08 507cc341ec doc: add example for conversion from slice expressions to array ptr
+ 2021-08-07 891547e2d4 doc/go1.17: fix a typo introduced in CL 335135
+ 2021-08-06 8eaf4d16bc make.bash: do not overwrite GO_LDSO if already set
+ 2021-08-06 63b968f4f8 doc/go1.17: clarify Modules changes
+ 2021-08-06 70546f6404 runtime: allow arm64 SEH to be called if illegal instruction
+ 2021-08-05 fd45e267c2 runtime: warn that KeepAlive is not an unsafe.Pointer workaround
+ 2021-08-04 6e738868a7 net/http: speed up and deflake TestCancelRequestWhenSharingConnection
+ 2021-08-02 8a7ee4c51e io/fs: don't use absolute path in DirEntry.Name doc
+ 2021-07-31 b8ca6e59ed all: gofmt
+ 2021-07-30 b7a85e0003 net/http/httputil: close incoming ReverseProxy request body
+ 2021-07-29 70fd4e47d7 runtime: avoid possible preemption when returning from Go to C
+ 2021-07-28 9eee0ed439 cmd/go: fix go.mod file name printed in error messages for replacements
+ 2021-07-28 b39e0f461c runtime: don't crash on nil pointers in checkptrAlignment
+ 2021-07-27 7cd10c1149 cmd/go: use .mod instead of .zip to determine if version has go.mod file
+ 2021-07-27 c8cf0f74e4 cmd/go: add missing flag in UsageLine
+ 2021-07-27 7ba8e796c9 testing: clarify T.Name returns a distinct name of the running test
+ 2021-07-27 33ff155970 go/types: preserve untyped constants on the RHS of a shift expression
+ 2021-07-26 840e583ff3 runtime: correct variable name in comment
+ 2021-07-26 bfbb288574 runtime: remove adjustTimers counter
+ 2021-07-26 9c81fd53b3 cmd/vet: add missing copyright header
Change-Id: Ia80604d24c6f4205265683024e3100769cf32065
When returning from Go to C, it was possible for the goroutine to be
preempted after calling unlockOSThread. This could happen when there
a context function installed by SetCgoTraceback set a non-zero context,
leading to a defer call in cgocallbackg1. The defer function wrapper,
introduced in 1.17 as part of the regabi support, was not nosplit,
and hence was a potential preemption point. If it did get preempted,
the G would move to a new M. It would then attempt to return to C
code on a different stack, typically leading to a SIGSEGV.
Fix this in a simple way by postponing the unlockOSThread until after
the other defer. Also check for the failure condition and fail early,
rather than waiting for a SIGSEGV.
Without the fix to cgocall.go, the test case fails about 50% of the
time on my laptop.
Fixes#47441
Change-Id: Ib8ca13215bd36cddc2a49e86698824a29c6a68ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/338197
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Conflicts:
- src/cmd/compile/internal/walk/builtin.go
On dev.typeparams, CL 330194 changed OCHECKNIL to not require manual
SetTypecheck(1) anymore; while on master, CL 331070 got rid of the
OCHECKNIL altogether by moving the check into the runtime support
functions.
- src/internal/buildcfg/exp.go
On master, CL 331109 refactored the logic for parsing the
GOEXPERIMENT string, so that it could be more easily reused by
cmd/go; while on dev.typeparams, several CLs tweaked the regabi
experiment defaults.
Merge List:
+ 2021-06-30 4711bf30e5 doc/go1.17: linkify "language changes" in the runtime section
+ 2021-06-30 ed56ea73e8 path/filepath: deflake TestEvalSymlinksAboveRoot on darwin
+ 2021-06-30 c080d0323b cmd/dist: pass -Wno-unknown-warning-option in swig_callback_lto
+ 2021-06-30 7d0e9e6e74 image/gif: fix typo in the comment (io.ReadByte -> io.ByteReader)
+ 2021-06-30 0fa3265fe1 os: change example to avoid deprecated function
+ 2021-06-30 d19a53338f image: add Uniform.RGBA64At and Rectangle.RGBA64At
+ 2021-06-30 c45e800e0c crypto/x509: don't fail on optional auth key id fields
+ 2021-06-29 f9d50953b9 net: fix failure of TestCVE202133195
+ 2021-06-29 e294b8a49e doc/go1.17: fix typo "MacOS" -> "macOS"
+ 2021-06-29 3463852b76 math/big: fix typo of comment (`BytesScanner` to `ByteScanner`)
+ 2021-06-29 fd4b587da3 cmd/compile: suppress details error for invalid variadic argument type
+ 2021-06-29 e2e05af6e1 cmd/internal/obj/arm64: fix an encoding error of CMPW instruction
+ 2021-06-28 4bb0847b08 cmd/compile,runtime: change unsafe.Slice((*T)(nil), 0) to return []T(nil)
+ 2021-06-28 1519271a93 spec: change unsafe.Slice((*T)(nil), 0) to return []T(nil)
+ 2021-06-28 5385e2386b runtime/internal/atomic: drop Cas64 pointer indirection in comments
+ 2021-06-28 956c81bfe6 cmd/go: add GOEXPERIMENT to `go env` output
+ 2021-06-28 a1d27269d6 cmd/go: prep for 'go env' refactoring
+ 2021-06-28 901510ed4e cmd/link/internal/ld: skip the windows ASLR test when CGO_ENABLED=0
+ 2021-06-28 361159c055 cmd/cgo: fix 'see gmp.go' to 'see doc.go'
+ 2021-06-27 c95464f0ea internal/buildcfg: refactor GOEXPERIMENT parsing code somewhat
+ 2021-06-25 ed01ceaf48 runtime/race: use race build tag on syso_test.go
+ 2021-06-25 d1916e5e84 go/types: in TestCheck/issues.src, import regexp/syntax instead of cmd/compile/internal/syntax
+ 2021-06-25 5160896c69 go/types: in TestStdlib, import from source instead of export data
+ 2021-06-25 d01bc571f7 runtime: make ncgocall a global counter
Change-Id: I1ce4a3b3ff7c824c67ad66dd27d9d5f1d25c0023
ncgocall was stored per M, runtime.NumCgoCall lost the counter when a M die.
Fixes#46789
Change-Id: I85831fbb2713f4c30d1800d07e1f47aa0031970e
GitHub-Last-Rev: cbc15fa870
GitHub-Pull-Request: golang/go#46842
Reviewed-on: https://go-review.googlesource.com/c/go/+/329729
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Alexander Rakoczy <alex@golang.org>
David Chase
Russ Cox
Michael Pratt
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Richard Wang
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Jes Cok
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