From: Otto Moerbeek <otto@drijf.net>
Subject: Re: timing lld --threads for fun and profit
To: Stuart Henderson <stu@spacehopper.org>
Cc: Landry Breuil <landry@openbsd.org>, robert@openbsd.org, tech@openbsd.org
Date: Sat, 9 Nov 2024 09:14:46 +0100

On Fri, Nov 08, 2024 at 01:01:50PM +0000, Stuart Henderson wrote:

> On 2024/11/08 13:26, Martin Pieuchot wrote:
> > On 08/11/24(Fri) 12:22, Landry Breuil wrote:
> > > [...] 
> > > someone(tm) should look into patching lld to avoid using more than
> > > MAX(ncpu,5) threads ? In the meantime, i'll probably fix the firefox
> > > ports to avoir using MAKE_JOBS for lld but cap it at 5.
> > 
> > Recent lld(1) include the following commits which limit the value to
> > 16 by default instead of the number of available CPUs.
> > 
> > See the following commits:
> > 
> > https://github.com/llvm/llvm-project/commit/a8788de1c3f3c8c3a591bd3aae2acee1b43b229a
> > https://github.com/llvm/llvm-project/commit/da68d2164efcc1f5e57f090e2ae2219056b120a0
> > 
> > Robert do you see the same with chromium?  Would it make sense to
> > backport these diff with a smaller value for OpenBSD?
> > 
> 
> Certainly helps for reorder_kernel.

It might be interesting to play with the number of malloc thread pools
as well.  There are undocumented malloc options to double/half the
number: + and -. Default is 8, maximum is 32. 

Which reminds me of the idea to try to make the default dependent on
the number of online CPUs. Never got around to trying that and see if
if it matters.

	-Otto

> 
> $ sysctl hw.{model,ncpu,version}
> hw.model=12th Gen Intel(R) Core(TM) i5-1245U
> hw.ncpu=12
> hw.version=ThinkPad T14 Gen 3
> 
> # \time -l /usr/libexec/reorder_kernel
>         7.30 real         6.86 user         3.92 sys
>     879280  maximum resident set size
>          0  average shared memory size
>          0  average unshared data size
>          0  average unshared stack size
>     147812  minor page faults
>      79421  major page faults
>          0  swaps
>      11833  block input operations
>      15643  block output operations
>          1  messages sent
>          0  messages received
>         45  signals received
>      46512  voluntary context switches
>       7353  involuntary context switches
> # vi Makefile
> [...]
> $ grep ^LINKFL Makefile
> LINKFLAGS=	-T ld.script -X --warn-common -nopie -Wl,--threads=5
> LINKFLAGS+=	-S
> # \time -l /usr/libexec/reorder_kernel
>         0.41 real         0.26 user         0.09 sys
>     100920  maximum resident set size
>          0  average shared memory size
>          0  average unshared data size
>          0  average unshared stack size
>      17119  minor page faults
>         10  major page faults
>          0  swaps
>          5  block input operations
>         78  block output operations
>          1  messages sent
>          0  messages received
>         28  signals received
>        189  voluntary context switches
>          2  involuntary context switches
>