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runtime: fix cputicks on x86 

See the following issue for context:
https://github.com/golang/go/issues/9729#issuecomment-74648287
In short, RDTSC can produce skewed results without preceding LFENCE/MFENCE.
Information on this matter is very scrappy in the internet.
But this is what linux kernel does (see rdtsc_barrier).
It also fixes the test program on my machine.

Update #9729

Change-Id: I3c1ffbf129fdfdd388bd5b7911b392b319248e68
Reviewed-on: https://go-review.googlesource.com/5033
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Dmitry Vyukov 2015-02-17 14:25:49 +03:00
parent 5868ce3519
commit 6e70fddec0
4 changed files with 50 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
src/runtime/asm_386.s
View File

@ -30,6 +30,19 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
CPUID
CMPL AX, $0
JE nocpuinfo
// Figure out how to serialize RDTSC.
// On Intel processors LFENCE is enough. AMD requires MFENCE.
// Don't know about the rest, so let's do MFENCE.
CMPL BX, $0x756E6547 // "Genu"
JNE notintel
CMPL DX, $0x49656E69 // "ineI"
JNE notintel
CMPL CX, $0x6C65746E // "ntel"
JNE notintel
MOVB $1, runtime·lfenceBeforeRdtsc(SB)
notintel:
MOVL $1, AX
CPUID
MOVL CX, runtime·cpuid_ecx(SB)
@ -868,9 +881,17 @@ TEXT runtime·gogetcallersp(SB),NOSPLIT,$0-8
MOVL AX, ret+4(FP)
RET
// int64 runtime·cputicks(void), so really
// void runtime·cputicks(int64 *ticks)
// func cputicks() int64
TEXT runtime·cputicks(SB),NOSPLIT,$0-8
TESTL $0x4000000, runtime·cpuid_edx(SB) // no sse2, no mfence
JEQ done
CMPB runtime·lfenceBeforeRdtsc(SB), $1
JNE mfence
BYTE $0x0f; BYTE $0xae; BYTE $0xe8 // LFENCE
JMP done
mfence:
BYTE $0x0f; BYTE $0xae; BYTE $0xf0 // MFENCE
done:
RDTSC
MOVL AX, ret_lo+0(FP)
MOVL DX, ret_hi+4(FP)

22
src/runtime/asm_amd64.s
View File

@ -30,6 +30,19 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
CPUID
CMPQ AX, $0
JE nocpuinfo
// Figure out how to serialize RDTSC.
// On Intel processors LFENCE is enough. AMD requires MFENCE.
// Don't know about the rest, so let's do MFENCE.
CMPL BX, $0x756E6547 // "Genu"
JNE notintel
CMPL DX, $0x49656E69 // "ineI"
JNE notintel
CMPL CX, $0x6C65746E // "ntel"
JNE notintel
MOVB $1, runtime·lfenceBeforeRdtsc(SB)
notintel:
MOVQ $1, AX
CPUID
MOVL CX, runtime·cpuid_ecx(SB)
@ -865,8 +878,15 @@ TEXT runtime·gogetcallersp(SB),NOSPLIT,$0-16
MOVQ AX, ret+8(FP)
RET
// int64 runtime·cputicks(void)
// func cputicks() int64
TEXT runtime·cputicks(SB),NOSPLIT,$0-0
CMPB runtime·lfenceBeforeRdtsc(SB), $1
JNE mfence
BYTE $0x0f; BYTE $0xae; BYTE $0xe8 // LFENCE
JMP done
mfence:
BYTE $0x0f; BYTE $0xae; BYTE $0xf0 // MFENCE
done:
RDTSC
SHLQ $32, DX
ADDQ DX, AX

7
src/runtime/runtime1.go
View File

@ -58,13 +58,6 @@ var (
iswindows int32
)
// Information about what cpu features are available.
// Set on startup in asm_{x86/amd64}.s.
var (
//cpuid_ecx uint32
//cpuid_edx uint32
)
func goargs() {
if GOOS == "windows" {
return

8
src/runtime/runtime2.go
View File

@ -562,12 +562,16 @@ var (
goos *int8
ncpu int32
iscgo bool
cpuid_ecx uint32
cpuid_edx uint32
signote note
forcegc forcegcstate
sched schedt
newprocs int32
// Information about what cpu features are available.
// Set on startup in asm_{x86,amd64}.s.
cpuid_ecx uint32
cpuid_edx uint32
lfenceBeforeRdtsc bool
)
/*