From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Subject: Re: [PATCH v4 1/5] nohz_full: add support for "cpu_isolated" mode
Date: Wed, 22 Jul 2015 12:28:34 -0700
Message-ID: <20150722192834.GA32511@linux.vnet.ibm.com>
References: <1436817481-8732-1-git-send-email-cmetcalf@ezchip.com>
 <1436817481-8732-2-git-send-email-cmetcalf@ezchip.com>
 <CALCETrWaBe10u1X+AqYM7TsbguL=aF-TyuN3xjqgR5Cg2=FiAA@mail.gmail.com>
 <55A4271B.9040506@ezchip.com>
 <CALCETrUMGx+ZC9rtAAErKaGg-LEtYXMOSVD1dCi7im3b1SMrVg@mail.gmail.com>
 <55AE993E.6040501@ezchip.com>
 <CALCETrVoHvofNHG81Q2Vb2i1qc7f2dy=qgkyb5NWNfUgYxhE8Q@mail.gmail.com>
 <20150721203622.GX3717@linux.vnet.ibm.com>
 <alpine.DEB.2.11.1507220856030.17411@east.gentwo.org>
Reply-To: paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <alpine.DEB.2.11.1507220856030.17411-wcBtFHqTun5QOdAKl3ChDw@public.gmane.org>
Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
Cc: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>, Chris Metcalf <cmetcalf-d5a29ZRxExrQT0dZR+AlfA@public.gmane.org>, Gilad Ben Yossef <giladb-d5a29ZRxExrQT0dZR+AlfA@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Viresh Kumar <viresh.kumar-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, "linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
List-Id: linux-api@vger.kernel.org

On Wed, Jul 22, 2015 at 08:57:45AM -0500, Christoph Lameter wrote:
> On Tue, 21 Jul 2015, Paul E. McKenney wrote:
> 
> > > > In the current version, there's also the vmstat_update() that
> > > > may schedule delayed work and interrupt the core again
> > > > shortly before realizing that there are no more counter updates
> > > > happening, at which point it quiesces.  Currently we handle
> > > > this in cpu_isolated mode simply by spinning and waiting for
> > > > the timer interrupts to complete.
> > >
> > > Perhaps we should fix that?
> >
> > Didn't Christoph Lameter fix this?  Or is this an additional problem?
> 
> Well the vmstat update must realize first that there are no outstanding
> updates before switching itself off. So typically there is one extra tick.
> But we could add another function that will simply fold the differential
> immediately and turn the kworker task in the expectation that the
> processor will stay quiet.

Got it, thank you!

								Thanx, Paul