From: Klemens Nanni <kn@openbsd.org>
Subject: Re: timing lld --threads for fun and profit
To: Landry Breuil <landry@openbsd.org>, robert@openbsd.org, tech@openbsd.org
Date: Tue, 12 Nov 2024 13:13:20 +0000

08.11.2024 16:01, Stuart Henderson пишет:
> 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

Can someone explain to me why this work when done in
	/usr/share/relink/kernel/GENERIC.MP/Makefile
but fails when done in

Index: sys/arch/amd64/conf/Makefile.amd64
===================================================================
RCS file: /cvs/src/sys/arch/amd64/conf/Makefile.amd64,v
diff -u -p -r1.137 Makefile.amd64
--- sys/arch/amd64/conf/Makefile.amd64	7 Jun 2024 05:17:34 -0000	1.137
+++ sys/arch/amd64/conf/Makefile.amd64	12 Nov 2024 12:49:03 -0000
@@ -86,6 +86,7 @@ COPTIMIZE?=	-O2
 CFLAGS=		${DEBUG} ${CWARNFLAGS} ${CMACHFLAGS} ${COPTIMIZE} ${COPTS} ${PIPE}
 AFLAGS=		-D_LOCORE -x assembler-with-cpp ${CWARNFLAGS} ${CMACHFLAGS}
 LINKFLAGS=	-T ld.script -X --warn-common -nopie
+LINKFLAGS+=	-Wl,--threads=5
 
 HOSTCC?=	${CC}
 HOSTED_CPPFLAGS=${CPPFLAGS:S/^-nostdinc$//}


$ cd /usr/src/sys/arch/amd64/compile/GENERIC.MP
$ make config ; make
config  -b /sys/arch/amd64/compile/GENERIC.MP/obj  -s /sys /sys/arch/amd64/conf/GENERIC.MP
$ make
[...]
LD="ld" sh makegap.sh 0xcccccccc gapdummy.o
ld -T ld.script -X --warn-common -nopie -Wl,--threads=5 -o bsd ${SYSTEM_HEAD} vers.o ${OBJS}
ld: error: unknown argument '-Wl,--threads=5'
*** Error 1 in /sys/arch/amd64/compile/GENERIC.MP (Makefile:2225 'bsd': @echo ld -T ld.script -X --warn-common -nopie -Wl,--threads=5 -o bsd...)


Using --threads=5 (i.e. without -Wl,) works in both places...

> # \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
> 

But then no longer has this effect.

I looked at 'ktrace -di -tx' for both and both run /usr/bin/ld,
so why does one fail, but not the other?  What am I missing?