linux-kernel - Re: [PATCH] An RCU for SMP with a single CPU garbage collector

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Message-ID: <20110309222914.GC1817@nowhere>
Date:	Wed, 9 Mar 2011 23:29:18 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Joe Korty <joe.korty@...r.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] An RCU for SMP with a single CPU garbage collector

On Mon, Mar 07, 2011 at 04:16:13PM -0500, Joe Korty wrote:
> On Mon, Mar 07, 2011 at 04:01:57PM -0500, Paul E. McKenney wrote:
> > Interesting!
> > 
> > But I would really prefer leveraging the existing RCU implementations
> > to the extent possible.  Are the user-dedicated CPUs able to invoke
> > system calls?  If so, something like Frederic's approach should permit
> > the existing RCU implementations to operate normally.  If not, what is
> > doing the RCU read-side critical sections on the dedicated CPUs?
> > 
> >                                                         Thanx, Paul
> 
> I haven't seen Frederic's patch.  Sorry I missed it!
> It might have saved a bit of work...

I'm sorry it's my fault, I should have Cc'ed you in my nohz task series.

It's here: https://lkml.org/lkml/2010/12/20/209 and the rcu changes
are spread in severals patches of the series. The idea is to
switch to extended quiescent state when we resume to userspace but
temporarily exit that state when we trigger an exception or an
irq. Then exit extended quiescent state when we enter the kernel
again.

I'll soon look at the last patchset you've posted.
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