linux-kernel - Re: [rfc][patch 2/2] x86

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Message-ID: <20070716094503.GC21464@wotan.suse.de>
Date:	Mon, 16 Jul 2007 11:45:03 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <ak@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc][patch 2/2] x86_64: FIFO ticket spinlocks

On Mon, Jul 16, 2007 at 11:26:46AM +0200, Ingo Molnar wrote:
> 
> * Nick Piggin <npiggin@...e.de> wrote:
> 
> > [...] trylock is more significantly slower, but they are relatively 
> > rare.
> 
> trylock is the main thing that the spinlock debugging code uses, and 
> SPINLOCK_DEBUG is frequently enabled by distro kernels. OTOH, the cost 
> looks like to be +5 instructions, right? Still ...

Which trylocks do you mean? The lockbreak spinlocks use trylock, but
those are not used with the ticket version.

I wouldn't be against adding an option between either of the lock
types, if there was value in it. But I would like to default ticket
locks to "y", at least in -rc kernels, in order to see if performance
goes down anywhere.
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