linux-kernel - Re: [PATCH] x86 rwsem optimization extreme

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Message-ID: <20100218105506.GA9944@elte.hu>
Date:	Thu, 18 Feb 2010 11:55:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Zachary Amsden <zamsden@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, "H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH] x86 rwsem optimization extreme


* Zachary Amsden <zamsden@...hat.com> wrote:

> >
> >Zachary Amsden<zamsden@...hat.com>  writes
> >>Incidentally, the cost of putting all the rwsem code inline, using the
> >>straightforward approach, for git-tip, using defconfig on x86_64 is
> >>3565 bytes / 20971778 bytes total, or 0.0168%, using gcc 4.4.3.
> >The nice advantage of putting lock code inline is that it gets
> >accounted to the caller in all profilers.
> >
> >-Andi
> >
> 
> Unfortunately, only for the uncontended case.  The hot case still ends up 
> in a call to the lock text section.

Nor is it really true that it's 'a problem for profilers' - call graph
recording works just fine, in fact it can be better for a call-graph record
if the locking sites are not sprinkled around the kernel and inlined.

	Ingo
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