linux-kernel - Re: cond_resched() and RCU CPU stall warnings

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Message-ID: <1394955020.19079.3.camel@marge.simpson.net>
Date:	Sun, 16 Mar 2014 08:30:20 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	peterz@...radead.org, mingo@...e.hu, josh@...htriplett.org,
	laijs@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: cond_resched() and RCU CPU stall warnings

On Sat, 2014-03-15 at 23:25 -0700, Paul E. McKenney wrote: 
> On Sun, Mar 16, 2014 at 07:09:42AM +0100, Mike Galbraith wrote:

> > Hm.  Since you only care about the case where your task is solo, how
> > about do racy checks, 100% accuracy isn't required is it?  Seems you
> > wouldn't want to unconditionally do that in tight loops.
> 
> And indeed, my current workaround unconditionally does schedule() one
> out of 256 loops.  I would do something similar here, perhaps based
> on per-CPU counters, perhaps even with racy accesses to avoid always
> doing preempt_disable()/preempt_enable().
> 
> Or did you have something else in mind?

Exactly what I meant, take a racy peek or two first.

-Mike

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