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cuonglm opened this issue Sep 20, 2021 · 6 comments
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cmd/go: fails to perform concurrent compilation on darwin/arm64 #48496

cuonglm opened this issue Sep 20, 2021 · 6 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. ToolSpeed
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Go1.18

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@cuonglm
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cuonglm commented Sep 20, 2021 •
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What version of Go are you using (go version)?

$ go version
go version devel go1.18-9e60c37147 Mon Sep 20 16:55:47 2021 +0000 darwin/arm64

Does this issue reproduce with the latest release?

Yes, both go1.16.8 and go1.17.1

What operating system and processor architecture are you using (go env)?

go env Output
$ go env

What did you do?

go build -n -a fmt 2>&1 | grep -c -- -c=

What did you expect to see?

grep -c -- -c= should return non-zero.

What did you see instead?

$ go1.16.8 build -n -a fmt 2>&1 | grep -c -- -c=
0
$ go1.17.1 build -n -a fmt 2>&1 | grep -c -- -c=
0
$ go build -n -a fmt 2>&1 | grep -c -- -c=  # Even with the fix from #48490
0

The problem seems that with arm64, there's -shared passed to the compiler:

go/src/cmd/go/internal/work/init.go

Line 173 in 79159f2

case "arm64":

cause gcBackendConcurrency return 1:

go/src/cmd/go/internal/work/gc.go

Line 214 in 79159f2

func gcBackendConcurrency(gcflags []string) int { 

$ GOOS=linux go1.17.1 build -n -a -x fmt 2>&1 | grep -c -- -c=
35
@cuonglm cuonglm added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 20, 2021
@cuonglm cuonglm mentioned this issue Sep 20, 2021
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@bcmills bcmills added this to the Backlog milestone Sep 20, 2021
@cuonglm cuonglm mentioned this issue Oct 4, 2021
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@josharian josharian mentioned this issue Oct 4, 2021
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@josharian
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I've manually reviewed all uses of ctxt.Flag_shared and they all look concurrency-safe to me. And I manually tested with the race detector and found no issues. I'm going to send a CL removing that particular check.

@gopherbot
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Change https://golang.org/cl/353871 mentions this issue: cmd/go,cmd/compile: re-enable concurrent compilation on darwin/arm64

@andig
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andig commented Oct 4, 2021

Funny enough the M1 shows all 4 fat cores at 100% when compiling gotip.

@josharian
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@andig that probably due to process-level concurrency.

@andig
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andig commented Oct 4, 2021 •
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Maybe. For what its worth: recompiling gotip with this CL applied does not provide a speedup afaikt:

❯ time GOROOT_BOOTSTRAP=/Users/andig/htdocs/golang ./make.bash
Building Go cmd/dist using /Users/andig/htdocs/golang. (devel go1.18-579ff8b131 Mon Oct 4 19:51:37 2021 +0000 darwin/arm64)
Building Go toolchain1 using /Users/andig/htdocs/golang.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building packages and commands for darwin/arm64.
---
Installed Go for darwin/arm64 in /Users/andig/htdocs/golang2
Installed commands in /Users/andig/htdocs/golang2/bin
GOROOT_BOOTSTRAP=/Users/andig/htdocs/golang ./make.bash  166.35s user 19.85s system 421% cpu 44.204 total

but:

❯ ~/htdocs/golang/bin/go build -n -a fmt 2>&1 | grep -c -- -c=
37

@josharian
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Yes, make.bash has ample process level parallelism. That is not true of all build graphs.

josharian added a commit to tailscale/go that referenced this issue Oct 7, 2021
@josharian
cmd/go,cmd/compile: re-enable concurrent compilation on darwin/arm64
399f0f1 
I've manually reviewed all uses of ctxt.Flag_shared for concurrency safety.
And I manually tested with the race detector and found no issues.
Allow -shared to be used with compiler concurrency,
thereby re-enabling concurrent compilation on darwin/arm64.

Fixes golang#48496

Change-Id: I8a084cb08e6050950e404ceb9bd7e3a20e07e9c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/353871
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit 579ff8b)
@dmitshur dmitshur added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels May 14, 2022
@dmitshur dmitshur modified the milestones: Backlog, Go1.18 May 14, 2022
@golang golang locked and limited conversation to collaborators May 14, 2023
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