tree eb5d6b9c5a173233b86baf6130b73d77b064e7d9
parent f07499aebcf5b1b8f09f27f705e1b6e463ecdba1
author Bruce Dawson <brucedawson@google.com> 1712698818 -0700
committer GN LUCI <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1712724937 +0000

Revert "Teach gn to handle systems with > 64 processors"

This reverts commit d9bbb45cbf7b2e54328b45e4573a107849d2db25.

Reason for revert: In the context of gn running on Chromium on modern
72+ core machines this CL causes a net slowdown. It causes gn to use
"too many" threads, leading to excessive lock contention, perhaps
exacerbated by using multiple NUMA nodes.

The original change measured only a tiny speedup so the potential
gains from reverting are much greater than the potential losses.

The original revert is here:

https://gn-review.git.corp.google.com/c/gn/+/17000

However when I resolved merge conflicts it got redirected from 17000
to 17020 and I'd like to land the version that has the merge conflicts
fixed.

Original change's description:
> Teach gn to handle systems with > 64 processors
>
> Previously, when run on Windows systems with > 64 logical processors,
> gn's calculation of the number of available processors (used to
> determine how many worker threads to create) under-counted the number of
> processors, thereby not making full use of the system's available
> processing power.
>
> This change corrects gn's count of available CPUs so that it can use all
> of the system's processors. In addition to creating the correct number
> of workers, this change also distributes created workers between
> processor groups, a necessary step when utilizing more than 64
> processors on Windows.
>
> On the 72-logical-processor P920, this change makes gn gen use all 36
> cores, rather than only 18.
>
> Bug: crbug.com/982982
> Change-Id: I40b40f4d34b634566991e4bebf686f48836445e8
> Reviewed-on: https://gn-review.googlesource.com/c/gn/+/5660
> Commit-Queue: Scott Graham <scottmg@chromium.org>
> Reviewed-by: Scott Graham <scottmg@chromium.org>

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: crbug.com/982982
Change-Id: I1ede6a0ec1eaa70b06061f2534232d2c5f0e47cb
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/17020
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Takuto Ikuta <tikuta@google.com>