From: Stuart Henderson <stu@spacehopper.org>
Subject: Re: timing lld --threads for fun and profit
To: Landry Breuil <landry@openbsd.org>, robert@openbsd.org, tech@openbsd.org
Date: Fri, 8 Nov 2024 13:01:50 +0000

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.

$ 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