linux-kernel - Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread wakeups

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Message-ID: <20140702175501.GW4603@linux.vnet.ibm.com>
Date:	Wed, 2 Jul 2014 10:55:01 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, riel@...hat.com, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	sbw@....edu
Subject: Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread
 wakeups

On Wed, Jul 02, 2014 at 07:26:00PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 02, 2014 at 10:08:38AM -0700, Paul E. McKenney wrote:
> > As were others, not that long ago.  Today is the first hint that I got
> > that you feel otherwise.  But it does look like the softirq approach to
> > callback processing needs to stick around for awhile longer.  Nice to
> > hear that softirq is now "sane and normal" again, I guess.  ;-)
> 
> Nah, softirqs are still totally annoying :-)

Name me one thing that isn't annoying.  ;-)

> So I've lost detail again, but it seems to me that on all CPUs that are
> actually getting ticks, waking tasks to process the RCU state is
> entirely over doing it. Might as well keep processing their RCU state
> from the tick as was previously done.

And that is in fact the approach taken by my patch.  For which I just
kicked off testing, so expect an update later today.  (And that -is-
optimistic!  A pessimistic viewpoint would hold that the patch would
turn out to be so broken that it would take -weeks- to get a fix!)

							Thanx, Paul

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