linux-kernel - Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"

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Message-ID: <20110526174301.GA9649@linux.vnet.ibm.com>
Date:	Thu, 26 May 2011 10:43:01 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Yinghai Lu <yinghai@...nel.org>, linux-kernel@...r.kernel.org,
	mingo@...hat.com, hpa@...or.com, tglx@...utronix.de
Subject: Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage
 based on semi-formal proof"

On Thu, May 26, 2011 at 07:25:53AM -0700, Paul E. McKenney wrote:
> On Thu, May 26, 2011 at 08:13:48AM +0200, Ingo Molnar wrote:
> > 
> > * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > rcu: Start RCU kthreads in TASK_INTERRUPTIBLE state
> > > 
> > > Upon creation, kthreads are in TASK_UNINTERRUPTIBLE state, which can
> > > result in softlockup warnings.  Because some of RCU's kthreads can
> > > legitimately be idle indefinitely, start them in TASK_INTERRUPTIBLE
> > > state in order to avoid those warnings.
> > > 
> > > Suggested-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > this should also solve load average artifacts - do not 
> > TASK_UNINTERRUPTIBLE tasks skew the load upwards?
> 
> Quite possibly -- in this case the artifacts would appear just after
> boot, and would disappear as soon as the RCU kthreads had something
> to do.

By the way, how would you like to proceed with the fixes thus far?
I have put them on -rcu for -next testing, FWIW.

							Thanx, Paul
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