linux-kernel - Re: [PATCH] force inlining of spinlock ops

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Message-ID: <20150512074443.GA724@gmail.com>
Date:	Tue, 12 May 2015 09:44:43 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Graf <tgraf@...g.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Bart Van Assche <bvanassche@....org>,
	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] force inlining of spinlock ops


* Denys Vlasenko <dvlasenk@...hat.com> wrote:

> With both gcc 4.7.2 and 4.9.2, sometimes gcc mysteriously doesn't inline
> very small functions we expect to be inlined. In particular,
> with this config: http://busybox.net/~vda/kernel_config
> there are more than a thousand copies of tiny spinlock-related functions:

That's an x86-64 allyesconfig AFAICS, right?

It's not mysterious, but an effect of -Os plus allowing GCC to do 
inlining heuristics:

  CONFIG_CC_OPTIMIZE_FOR_SIZE=y
  CONFIG_OPTIMIZE_INLINING=y

Does the problem go away if you unset of these config options?

Furtermore, what is the size win on x86 defconfig with these options 
set? allyesconfig has all sorts of crazy stuff enabled while defconfig 
on x86 tries to track typical distro configs.

Thanks,

	Ingo
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