linux-kernel - Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Message-ID: <20090111181307.GM26290@one.firstfloor.org>
Date:	Sun, 11 Jan 2009 19:13:07 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

On Sun, Jan 11, 2009 at 12:26:41PM +0000, David Woodhouse wrote:
>   - Unconditionally have 'inline' meaning 'always_inline'. If we say it,
>     we should mean it.
> 
>   - Resist the temptation to use -fno-inline-functions. Allow GCC to
>     inline other things if it wants to.

The proposal was to use -fno-inline-functions-called-once (but 
the resulting numbers were not promising)

We've never allowed gcc to inline any other functions not marked
inline explicitely because that's not included in -O2. 

>   - Reduce the number of unnecessary 'inline' markers, and have a policy
>     that the use of 'inline' should be accompanied by either a GCC PR#
>     or an explanation of why we couldn't reasonably have expected GCC to
>     get this particular case right.
> 
>   - Have a similar policy of PR# or explanation for 'uninline' too.
> 
> I don't think we should just give up on GCC ever getting it right. That
> way lies madness. As we've often found in the past. 

It sounds like you're advocating to set -O3/-finline-functions
by default.   Not sure that's a good idea.

-Andi

-- 
ak@...ux.intel.com
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