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runtime: on linux/PPC64, usleep computes incorrect tv_nsec parameter #56374

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pmur opened this issue Oct 21, 2022 · 3 comments
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runtime: on linux/PPC64, usleep computes incorrect tv_nsec parameter #56374

pmur opened this issue Oct 21, 2022 · 3 comments
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arch-ppc64x compiler/runtime Issues related to the Go compiler and/or runtime.

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pmur commented Oct 21, 2022

While investigating high context switch numbers in the runtime, it was discovered the PPC64 implementation of usleep passes incorrect values to the tv_nsec parameter of the nanosleep syscall. It fails to convert the remainder microseconds to nanoseconds. This can be observed with perf stat on simple benchmarks. The high context-switch rate was related to sysmon polling at 1000x the desired rate.

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@pmur pmur added arch-ppc64x compiler/runtime Issues related to the Go compiler and/or runtime. labels Oct 21, 2022
@pmur pmur self-assigned this Oct 21, 2022
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Change https://go.dev/cl/444735 mentions this issue: runtime: fix usleep on PPC64

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pmur commented Oct 24, 2022

@gopherbot please consider a backport to 1.18 and 1.19. This is a subtle bug.

This was referenced Oct 24, 2022
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Backport issue(s) opened: #56396 (for 1.18), #56397 (for 1.19).

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

romaindoumenc pushed a commit to TroutSoftware/go that referenced this issue Nov 3, 2022
@pmur @romaindoumenc
runtime: fix usleep on linux/PPC64
27cde35 
The existing implementation fails to convert the remainder
microseconds to nanoseconds. This causes sysmon to consume
much more cpu, and generate lots of context switches.

We can also do a little better here to avoid division by a
constant. I used go to determine the magic numbers.

Fixes golang#56374

Change-Id: I2e37ec218b9027efab6db4634eed1504c0c1b3c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/444735
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
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arch-ppc64x compiler/runtime Issues related to the Go compiler and/or runtime.
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