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Date: Mon, 25 Jul 2011 09:46:19 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>, linux-kernel@vger.kernel.org,
        Bharata B Rao <bharata@linux.vnet.ibm.com>,
        Dhaval Giani <dhaval.giani@gmail.com>,
        Balbir Singh <bsingharora@gmail.com>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        Srivatsa Vaddagiri <vatsa@in.ibm.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
        Ingo Molnar <mingo@elte.hu>, Pavel Emelyanov <xemul@openvz.org>,
        Jason Baron <jbaron@redhat.com>
Subject: Re: [patch 00/18] CFS Bandwidth Control v7.2
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On Mon, Jul 25, 2011 at 06:28:31PM +0200, Peter Zijlstra wrote:
> On Mon, 2011-07-25 at 09:21 -0700, Paul E. McKenney wrote:
> > On Mon, Jul 25, 2011 at 05:00:41PM +0200, Peter Zijlstra wrote:
> > > On Mon, 2011-07-25 at 16:58 +0200, Peter Zijlstra wrote:
> > > > +               rcu_read_lock();
> > > > +               ret = walk_tg_tree_from(tg, tg_set_cfs_period_down, NULL, &period);
> > > > +               rcu_read_unlock(); 
> > > 
> > > rcu over a mutex doesn't really work in mainline, bah.. 
> > 
> > SRCU can handle that situation, FWIW.  But yes, blocking in an RCU
> > read-side critical section is a no-no.
> 
> Yeah, I know, but didn't notice until after I sent.. SRCU isn't useful
> though, way too slow due to lacking srcu_call().

Good point.  How frequently would a call_srcu() be invoked?

In other words, would a really crude hack involving a globally locked
per-srcu_struct callback list and a per-srcu_struct kernel thread be
helpful, or would a slightly less-crude hack involving a per-CPU callback
list be required?

							Thanx, Paul