From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc: Force inlining of csum_add()
Date: Wed, 12 May 2021 13:21:03 -0500 [thread overview]
Message-ID: <20210512182103.GX10366@gate.crashing.org> (raw)
In-Reply-To: <2623fe98-7a73-f7a2-bcba-2d668d00ffd0@csgroup.eu>
On Wed, May 12, 2021 at 04:43:33PM +0200, Christophe Leroy wrote:
> Le 12/05/2021 à 16:31, Segher Boessenkool a écrit :
> >On Wed, May 12, 2021 at 02:56:56PM +0200, Christophe Leroy wrote:
> >>Le 11/05/2021 à 12:51, Segher Boessenkool a écrit :
> >>>Something seems to have decided this asm is more expensive than it is.
> >>>That isn't always avoidable -- the compiler cannot look inside asms --
> >>>but it seems it could be improved here.
> >>>
> >>>Do you have (or can make) a self-contained testcase?
> >>
> >>I have not tried, and I fear it might be difficult, because on a kernel
> >>build with dozens of calls to csum_add(), only ip6_tunnel.o exhibits such
> >>an issue.
> >
> >Yeah. Sometimes you can force some of the decisions, but that usually
> >requires knowing too many GCC internals :-/
> >
> >>>>And there is even one completely unused instance of csum_add().
> >>>
> >>>That is strange, that should never happen.
> >>
> >>It seems that several .o include unused versions of csum_add. After the
> >>final link, one remains (in addition to the used one) in vmlinux.
> >
> >But it is a static function, so it should not end up in any object file
> >where it isn't used.
>
> Well .... did I dream ?
>
> Now I only find one extra .o with unused csum_add() : That's
> net/ipv6/exthdrs.o
> It matches the one found in vmlinux.
>
> Are you interested in -fdump-tree-einline-all for that one as well ?
Sure. Hopefully it will show more :-)
Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc: Force inlining of csum_add()
Date: Wed, 12 May 2021 13:21:03 -0500 [thread overview]
Message-ID: <20210512182103.GX10366@gate.crashing.org> (raw)
In-Reply-To: <2623fe98-7a73-f7a2-bcba-2d668d00ffd0@csgroup.eu>
On Wed, May 12, 2021 at 04:43:33PM +0200, Christophe Leroy wrote:
> Le 12/05/2021 à 16:31, Segher Boessenkool a écrit :
> >On Wed, May 12, 2021 at 02:56:56PM +0200, Christophe Leroy wrote:
> >>Le 11/05/2021 à 12:51, Segher Boessenkool a écrit :
> >>>Something seems to have decided this asm is more expensive than it is.
> >>>That isn't always avoidable -- the compiler cannot look inside asms --
> >>>but it seems it could be improved here.
> >>>
> >>>Do you have (or can make) a self-contained testcase?
> >>
> >>I have not tried, and I fear it might be difficult, because on a kernel
> >>build with dozens of calls to csum_add(), only ip6_tunnel.o exhibits such
> >>an issue.
> >
> >Yeah. Sometimes you can force some of the decisions, but that usually
> >requires knowing too many GCC internals :-/
> >
> >>>>And there is even one completely unused instance of csum_add().
> >>>
> >>>That is strange, that should never happen.
> >>
> >>It seems that several .o include unused versions of csum_add. After the
> >>final link, one remains (in addition to the used one) in vmlinux.
> >
> >But it is a static function, so it should not end up in any object file
> >where it isn't used.
>
> Well .... did I dream ?
>
> Now I only find one extra .o with unused csum_add() : That's
> net/ipv6/exthdrs.o
> It matches the one found in vmlinux.
>
> Are you interested in -fdump-tree-einline-all for that one as well ?
Sure. Hopefully it will show more :-)
Segher
next prev parent reply other threads:[~2021-05-12 20:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 6:08 [PATCH] powerpc: Force inlining of csum_add() Christophe Leroy
2021-05-11 6:08 ` Christophe Leroy
2021-05-11 10:51 ` Segher Boessenkool
2021-05-11 10:51 ` Segher Boessenkool
2021-05-12 12:56 ` Christophe Leroy
2021-05-12 12:56 ` Christophe Leroy
2021-05-12 14:31 ` Segher Boessenkool
2021-05-12 14:31 ` Segher Boessenkool
2021-05-12 14:43 ` Christophe Leroy
2021-05-12 14:43 ` Christophe Leroy
2021-05-12 18:21 ` Segher Boessenkool [this message]
2021-05-12 18:21 ` Segher Boessenkool
2021-06-18 3:51 ` Michael Ellerman
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