Date: Wed, 2 Jul 2014 10:57:22 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
        rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
        dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
        sbw@mit.edu
Subject: Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread
 wakeups
Message-ID: <20140702175722.GX4603@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <20140627142038.GA22942@linux.vnet.ibm.com>
 <20140702123412.GD19379@twins.programming.kicks-ass.net>
 <20140702153915.GQ4603@linux.vnet.ibm.com>
 <20140702160412.GO19379@twins.programming.kicks-ass.net>
 <20140702170838.GS4603@linux.vnet.ibm.com>
 <20140702172600.GR19379@twins.programming.kicks-ass.net>
 <53B44182.4090107@redhat.com>
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On Wed, Jul 02, 2014 at 01:29:38PM -0400, Rik van Riel wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 07/02/2014 01:26 PM, 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 :-)
> > 
> > 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.
> 
> For CPUs that are not getting ticks (eg. because they are idle),
> is it worth waking up anything on that CPU, or would it make more
> sense to simply process their RCU callbacks on a different CPU,
> if there aren't too many pending?

Give or take the number of wakeups generated...  ;-)

							Thanx, Paul

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