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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug bootstrap/96794] --with-build-config=bootstrap-lto-lean with
 --enable-link-mutex leads to poor LTRANS utilization
Date: Wed, 26 Aug 2020 10:13:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96794

--- Comment #4 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
> > For jobserver they are still running even though they sleep.
> Aha, so it is extra locking mechanizm we add without jobserver
> knowledge.

It's unrelated to jobserver, one can enable it with configure option mentio=
ned
in the title.

> >=20
> >=20
> > > We limit makefile to link a binary at a time to avoid Richi's box get=
ting
> > > out of memory, right?
> >=20
> > No. It's because we want to have a reasonable contrains which is right =
now 8GB.
> > Without --enable-link-mutex, we would consume ~ 10 x 1.3 GB (plus WPA p=
arallel
> > streaming peak), which is probably not desired.
>=20
> 10x1.3GB will get consumed only if the building machine has 10 threads.

Typical OBS machine used for package build is either 8 (required minimum) or
16.=20

> I wonder if the jobserver WPA streaming integration will happen this
> year, with that snd some patches to WPA memory use we could fit in 8GB
> unless very large parallelism is configured.
>=20
> I suppose only really effective solution would to teach the jobserver
> that some jobs are "big" and consume multiple tokens, that is WPA, while
> other jobs like ltranses and streaming are small.
>=20
> This is of course still not very pretty, but it is impossible to tell in
> advance what job is big and what job is small.

Sure, it's all quite compilicated. One needs to negotiate with jobserver :)

I'm going to collect graph w/o --enable-link-mutex on my machine.

>=20
> Honza=