linux-kernel - Re: queued spinlock code and results

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Date:	Wed, 11 Jul 2007 06:51:12 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: queued spinlock code and results

On Tue, Jul 10, 2007 at 07:26:10PM -0700, Christoph Lameter wrote:
> On Wed, 11 Jul 2007, Nick Piggin wrote:
> 
> > BTW. some advanced congestion algorithms like HBO may find these ticket
> > locks useful because you can see immediately how many CPUs are contending
> > the lock, and spinners know how many CPUs are in front of them. That info
> > could be fed into the spin backoff scheme.
> 
> That would mean having to keep a lot of status information for a spinlock. 
> Gets pretty complicated.

Did you look at the implementation? It takes 2 bytes on x86 and is almost
the same code size and speed as the existing locks.

> The RT tree already converts spinlocks to sleeping locks? If we want to be 
> that complicated then maybe going with one sophisticated lock type for all 
> would be the solution.

I don't want to convert spinlocks to sleeping locks though.
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