linux-kernel - Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather than rcu

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Message-ID: <20080825200509.GH6745@linux.vnet.ibm.com>
Date:	Mon, 25 Aug 2008 13:05:09 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Ingo Molnar <mingo@...e.hu>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andi Kleen <andi@...stfloor.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather
	than rcu

On Mon, Aug 25, 2008 at 10:44:03AM -0500, Christoph Lameter wrote:
> Paul E. McKenney wrote:
> 
> > But I am not sure that this gets the grace periods to go fast enough to
> > cover Christoph's use case -- he seems to be in a "faster is better"
> > space rather than in an "at least this fast" space.  Still, it would
> > likely help in some important cases.
> 
> I think there was an AIM9 regression in the close/open tests when the struct
> file was switched to RCU. That test could be run with various intervals to
> figure out if a shorter RCU period is beneficial and how short an RCU period
> is needed to avoid the regression.

Well, with some luck, I can get an RCU implementation that allows the
grace-period duration to be varied, which would allow someone to check
the AIM9 regression.

							Thanx, Paul
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