Re: [PATCH v4 1/5] nohz_full: add support for "cpu_isolated" mode

From	Christoph Lameter <cl@linux.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 1/5] nohz_full: add support for "cpu_isolated" mode
Date	2015-07-22 16:00 +0200
Message-ID	<pP2IV-bi-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <pLTLQ-24J-11@gated-at.bofh.it> <pLTLQ-24J-9@gated-at.bofh.it> <pOLf4-yk-11@gated-at.bofh.it> <pOLoK-JK-15@gated-at.bofh.it> <pOMuu-2gx-3@gated-at.bofh.it>
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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.

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Re: [PATCH v4 1/5] nohz_full: add support for "cpu_isolated" mode Christoph Lameter <cl@linux.com> - 2015-07-22 16:00 +0200

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