| commit | 123f7dd3e1eb90825ece57b8dde39438ca34f150 | [log] [tgz] |
|---|---|---|
| author | Cherry Zhang <cherryyz@google.com> | Tue Feb 11 18:54:30 2020 -0500 |
| committer | Cherry Zhang <cherryyz@google.com> | Thu Feb 13 19:41:53 2020 +0000 |
| tree | 87c73b63b74568419b164d64b4f5509ffaad9aae | |
| parent | a0c9fb6bd359f111f19176ff176244b91a3e7eaa [diff] |
runtime: zero upper bit of Y registers in asyncPreempt on darwin/amd64 Apparently, the signal handling code path in darwin kernel leaves the upper bits of Y registers in a dirty state, which causes many SSE operations (128-bit and narrower) become much slower. Clear the upper bits to get to a clean state. We do it at the entry of asyncPreempt, which is immediately following exiting from the kernel's signal handling code, if we actually injected a call. It does not cover other exits where we don't inject a call, e.g. failed preemption, profiling signal, or other async signals. But it does cover an important use case of async signals, preempting a tight numerical loop, which we introduced in this cycle. Running the benchmark in issue #37174: name old time/op new time/op delta Fast-8 90.0ns ± 1% 46.8ns ± 3% -47.97% (p=0.000 n=10+10) Slow-8 188ns ± 5% 49ns ± 1% -73.82% (p=0.000 n=10+9) There is no more slowdown due to preemption signals. For #37174. Change-Id: I8b83d083fade1cabbda09b4bc25ccbadafaf7605 Reviewed-on: https://go-review.googlesource.com/c/go/+/219131 Run-TryBot: Cherry Zhang <cherryyz@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>
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