linux-kernel - Re: [PATCH] x86/processor.h: Force inlining of cpu

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Date:	Fri, 25 Sep 2015 13:44:23 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/processor.h: Force inlining of cpu_relax()

On Thu, Sep 24, 2015 at 02:02:29PM +0200, Denys Vlasenko wrote:
> On x86, cpu_relax() simply calls rep_nop(), which generates one
> instruction, PAUSE (aka REP NOP).
> 
> With this config:
> http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os
> gcc-4.7.2 does not always inline rep_nop(): it generates
> several copies of this:
> 
> <rep_nop> (16 copies, 194 calls):
>        55                      push   %rbp
>        48 89 e5                mov    %rsp,%rbp
>        f3 90                   pause
>        5d                      pop    %rbp
>        c3                      retq
> 
> See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122
> 
> This patch fixes this via s/inline/__always_inline/
> on rep_nop() and cpu_relax().
> (Forcing inlining only on rep_nop() causes gcc to
> deinline cpu_relax(), with almost no change in generated code).
> 
>     text     data      bss       dec     hex filename
> 88118971 19905208 36421632 144445811 89c1173 vmlinux.before
> 88118139 19905208 36421632 144444979 89c0e33 vmlinux

Looks ok to me, text even grows smaller.

Acked-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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