It is faster to execute
MOVQ AX,(DI)
MOVQ AX,8(DI)
MOVQ AX,16(DI)
MOVQ AX,24(DI)
ADDQ $32,DI
than
STOSQ
STOSQ
STOSQ
STOSQ
However, in order to be able to jump into
the middle of a block of MOVQs, the call
site needs to pre-adjust DI.
If we're clearing a small area, the cost
of that DI pre-adjustment isn't repaid.
This CL switches the DUFFZERO implementation
to use a hybrid strategy, in which small
clears use STOSQ as before, but large clears
use mostly MOVQ/ADDQ blocks.
benchmark old ns/op new ns/op delta
BenchmarkClearFat8 0.55 0.55 +0.00%
BenchmarkClearFat12 0.82 0.83 +1.22%
BenchmarkClearFat16 0.55 0.55 +0.00%
BenchmarkClearFat24 0.82 0.82 +0.00%
BenchmarkClearFat32 2.20 1.94 -11.82%
BenchmarkClearFat40 1.92 1.66 -13.54%
BenchmarkClearFat48 2.21 1.93 -12.67%
BenchmarkClearFat56 3.03 2.20 -27.39%
BenchmarkClearFat64 3.26 2.48 -23.93%
BenchmarkClearFat72 3.57 2.76 -22.69%
BenchmarkClearFat80 3.83 3.05 -20.37%
BenchmarkClearFat88 4.14 3.30 -20.29%
BenchmarkClearFat128 5.54 4.69 -15.34%
BenchmarkClearFat256 9.95 9.09 -8.64%
BenchmarkClearFat512 18.7 17.9 -4.28%
BenchmarkClearFat1024 36.2 35.4 -2.21%
Change-Id: Ic786406d9b3cab68d5a231688f9e66fcd1bd7103
Reviewed-on: https://go-review.googlesource.com/2585
Reviewed-by: Keith Randall <khr@golang.org>
This makes it easier to experiment with alternative implementations.
While we're here, update the comments.
No functional changes. Passes toolstash -cmp.
Change-Id: I428535754908f0fdd7cc36c214ddb6e1e60f376e
Reviewed-on: https://go-review.googlesource.com/8310
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Josh Bleecher Snyder