linux-kernel - Re: [tip:core/locking] x86/smp: Move waiting on contended ticket lock out of line

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Date:	Fri, 15 Feb 2013 16:57:57 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>, rostedt@...dmiss.org,
	aquini@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michel Lespinasse <walken@...gle.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/locking] x86/smp: Move waiting on contended ticket
 lock out of line


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Btw, it may end up that almost nobody cares. Modern CPU's are 
> really good at handling the straightforward "save/restore to 
> stack" instructions. One of the reasons I care is not 
> performance per se, butu the fact that I still look at asm 
> code every time I do any performance profiling, and it's 
> absolutely horrible to see the code when you see "ugh, that's 
> pointless". I'm sensitive to the spinlocks in particular, 
> because we've gone back and forth on inlining them before, so 
> I've seen this. But right now I don't think we inline the lock 
> under normal configs *anyway*, so I guess it doesn't much 
> matter.

Yes, right now we only inline non-debug spin_unlock() and 
spin_unlock_irq() [on !PREEMPT] - because that was an 
unconditional win.

Thanks,

	Ingo
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