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runtime: x86 CPU feature optimizations dropped in Go 1.17 #48406

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aclements opened this issue Sep 15, 2021 · 8 comments
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runtime: x86 CPU feature optimizations dropped in Go 1.17 #48406

aclements opened this issue Sep 15, 2021 · 8 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.18

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@aclements
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CL 344329 caused the runtime to no longer detect POPCNT, SSE 4.1, or FMA support on amd64. This affects the performance of math/bits.OnesCount, math.FMA, and most of the rounding functions in math.

This CL was released as part of Go 1.17, so this may be worth a back-port, or maybe the risk is too high for not enough reward.

/cc @martisch
@aclements aclements added the NeedsFix The path to resolution is known, but the work has not been done. label Sep 15, 2021
@aclements aclements added this to the Go1.18 milestone Sep 15, 2021
@aclements
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@gopherbot , please backport to Go 1.17.

@gopherbot
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Backport issue(s) opened: #48407 (for 1.17).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

@gopherbot gopherbot mentioned this issue Sep 15, 2021
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@aclements
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This is fixed by CL 350151.

nimelehin added a commit to nimelehin/go that referenced this issue Sep 15, 2021
@nimelehin
runtime: fix setting of cpu features for amd64
91c7321 
Because of wrong case of letters, the cpu features flags were not
set properly for amd64.

Fixes golang#48406
@nimelehin nimelehin mentioned this issue Sep 15, 2021
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@gopherbot
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Change https://golang.org/cl/350151 mentions this issue: runtime: fix setting of cpu features for amd64

@martisch
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martisch commented Sep 15, 2021 •
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Sorry.

Why do we think this made it to go1.17? The CL that caused the regression was submitted August 23 after go1.18 tree opened. I cant see that change in the go1.17 release branch:

go/src/runtime/proc.go

Line 637 in 21a4e67

x86HasPOPCNT = cpu.X86.HasPOPCNT

@aclements
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Why do we think this made it to go1.17?

Sorry, I was mistaken about that.

@cespare
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cespare commented Sep 15, 2021

Worth adding GOARCH/GOOS string constants somewhere?

@aclements
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Possibly. We already have goarch.ArchFamily and goarch.Is* constants, but the former is a bit of a mouthful and the latter are defined as 0/1 numeric constants, which are annoying to use in contexts like this. We also don't have an equivalent of goarch.ArchFamily for goos. Maybe we should just clean all of that up.

@komuw komuw mentioned this issue Sep 16, 2021
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runtime: fix setting of cpu features for amd64 nimelehin/go
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@martisch @cespare @aclements @gopherbot