linux-kernel - Re: [PATCH 7/8] locking: Introduce qrwlock

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Date:	Thu, 13 Feb 2014 18:26:57 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@...com>
Cc:	linux-kernel@...r.kernel.org, Jason Low <jason.low2@...com>,
	mingo@...nel.org, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, tglx@...utronix.de, riel@...hat.com,
	akpm@...ux-foundation.org, davidlohr@...com, hpa@...or.com,
	andi@...stfloor.org, aswin@...com, scott.norton@...com,
	chegu_vinod@...com
Subject: Re: [PATCH 7/8] locking: Introduce qrwlock

On Thu, Feb 13, 2014 at 05:35:46PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 11, 2014 at 03:12:59PM -0500, Waiman Long wrote:
> > Using the same locktest program to repetitively take a single rwlock with
> > programmable number of threads and count their execution times. Each
> > thread takes the lock 5M times on a 4-socket 40-core Westmere-EX
> > system. I bound all the threads to different CPUs with the following
> > 3 configurations:
> > 
> >  1) Both CPUs and lock are in the same node
> >  2) CPUs and lock are in different nodes
> >  3) Half of the CPUs are in same node as the lock & the other half
> >     are remote
> 
> I can't find these configurations in the below numbers; esp the first is
> interesting because most computers out there have no nodes.
> 
> > Two types of qrwlock are tested:
> >  1) Use MCS lock
> >  2) Use ticket lock
> 
> arch_spinlock_t; you forget that if you change that to an MCS style lock
> this one goes along for free.

Furthermore; comparing the current rwlock to the ticket-rwlock already
shows an improvement, so on that aspect its worth it as well.

And there's also the paravirt people to consider; a fair rwlock will
make them unhappy; and I'm hoping that their current paravirt ticket
stuff is sufficient to deal with the ticket-rwlock without them having
to come and wreck things again.

Similarly; qspinlock needs paravirt support.


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