From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Joel Stanley <joel@jms.id.au>, Arnd Bergmann <arnd@arndb.de>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-arch@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] asm-generic: Force inlining of get_order() to work around gcc10 poor decision
Date: Mon, 19 Oct 2020 03:32:25 -0500 [thread overview]
Message-ID: <20201019083225.GN2672@gate.crashing.org> (raw)
In-Reply-To: <0bd0afae-f043-2811-944b-c94d90e231d2@csgroup.eu>
On Mon, Oct 19, 2020 at 07:50:41AM +0200, Christophe Leroy wrote:
> Le 19/10/2020 à 06:55, Joel Stanley a écrit :
> >>In the old days, marking a function 'static inline' was forcing
> >>GCC to inline, but since commit ac7c3e4ff401 ("compiler: enable
> >>CONFIG_OPTIMIZE_INLINING forcibly") GCC may decide to not inline
> >>a function.
> >>
> >>It looks like GCC 10 is taking poor decisions on this.
> >1952 bytes smaller with your patch applied. Did you raise this with
> >anyone from GCC?
>
> Yes I did, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445
>
> For the time being, it's at a standstill.
The kernel should just use __always_inline if that is what it *wants*;
that is true here most likely. GCC could perhaps improve its heuristics
so that it no longer thinks these functions are often too big for
inlining (they *are* pretty big, but not after basic optimisations with
constant integer arguments).
Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: linux-arch@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Joel Stanley <joel@jms.id.au>,
Andrew Morton <akpm@linux-foundation.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] asm-generic: Force inlining of get_order() to work around gcc10 poor decision
Date: Mon, 19 Oct 2020 03:32:25 -0500 [thread overview]
Message-ID: <20201019083225.GN2672@gate.crashing.org> (raw)
In-Reply-To: <0bd0afae-f043-2811-944b-c94d90e231d2@csgroup.eu>
On Mon, Oct 19, 2020 at 07:50:41AM +0200, Christophe Leroy wrote:
> Le 19/10/2020 à 06:55, Joel Stanley a écrit :
> >>In the old days, marking a function 'static inline' was forcing
> >>GCC to inline, but since commit ac7c3e4ff401 ("compiler: enable
> >>CONFIG_OPTIMIZE_INLINING forcibly") GCC may decide to not inline
> >>a function.
> >>
> >>It looks like GCC 10 is taking poor decisions on this.
> >1952 bytes smaller with your patch applied. Did you raise this with
> >anyone from GCC?
>
> Yes I did, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445
>
> For the time being, it's at a standstill.
The kernel should just use __always_inline if that is what it *wants*;
that is true here most likely. GCC could perhaps improve its heuristics
so that it no longer thinks these functions are often too big for
inlining (they *are* pretty big, but not after basic optimisations with
constant integer arguments).
Segher
next prev parent reply other threads:[~2020-10-19 9:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-17 15:55 [PATCH] asm-generic: Force inlining of get_order() to work around gcc10 poor decision Christophe Leroy
2020-10-17 15:55 ` Christophe Leroy
2020-10-19 4:55 ` Joel Stanley
2020-10-19 4:55 ` Joel Stanley
2020-10-19 5:50 ` Christophe Leroy
2020-10-19 5:50 ` Christophe Leroy
2020-10-19 8:32 ` Segher Boessenkool [this message]
2020-10-19 8:32 ` Segher Boessenkool
2020-10-19 8:54 ` Christophe Leroy
2020-10-19 8:54 ` Christophe Leroy
2020-10-19 17:55 ` Segher Boessenkool
2020-10-19 17:55 ` Segher Boessenkool
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