linux-kernel - Re: [rfc][patch] queued spinlocks (i386)

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Message-ID: <20070323110224.GP2986@holomorphy.com>
Date:	Fri, 23 Mar 2007 04:02:24 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ravikiran G Thirumalai <kiran@...lex86.org>
Subject: Re: [rfc][patch] queued spinlocks (i386)

On Fri, Mar 23, 2007 at 11:04:18AM +0100, Ingo Molnar wrote:
>> isnt this patented by MS? (which might not worry you SuSE/Novell guys, 
>> but it might be a worry for the rest of the world ;-)

On Fri, Mar 23, 2007 at 11:32:44AM +0100, Nick Piggin wrote:
> Hmm, it looks like they have implemented a system where the spinning
> cpu sleeps on a per-CPU variable rather than the lock itself, and
> the releasing cpu writes to that variable to wake it.  They do this
> so that spinners don't continually perform exclusive->shared
> transitions on the lock cacheline. They call these things queued
> spinlocks.  They don't seem to be very patent worthy either, but
> maybe it is what you're thinking of?

Those exclusive-to-shared transitions are among the cacheline transfers
typically accounted to the algorithms in their complexity analyses.


-- wli
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