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Message-ID: <20150716003218.GA15221@milliways>
Date: Thu, 16 Jul 2015 01:32:18 +0100
From: Ken Moffat <zarniwhoop@...world.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Jeff Epler <jepler@...ythonic.net>
Subject: Re: CONFIG_NO_HZ_FULL restricts cpu usage to the equivalent of one
in 4.2
On Wed, Jul 15, 2015 at 09:11:46PM +0200, Frederic Weisbecker wrote:
> 2015-07-15 18:27 GMT+02:00 Ken Moffat <zarniwhoop@...world.com>:
> >
> > The config differences follow. Perhaps it is actually one of the
> > subsequent choices that is the problem. And I guess it could still
> > be a gcc-5.1 issue.
> >
> > --- config-4.2-initial 2015-07-15 16:25:12.548005751 +0100
> > +++ config-4.2-speed-ok 2015-07-15 17:00:50.919998703 +0100
> > @@ -104,11 +104,8 @@
> > CONFIG_TICK_ONESHOT=y
> > CONFIG_NO_HZ_COMMON=y
> > # CONFIG_HZ_PERIODIC is not set
> > -# CONFIG_NO_HZ_IDLE is not set
> > -CONFIG_NO_HZ_FULL=y
> > -CONFIG_NO_HZ_FULL_ALL=y
>
> You had CONFIG_NO_HZ_FULL_ALL enabled? Because that would indeed
> produce that effect since it isolates all CPUs but 0 off sched
> domains.
>
> Which means that basically only CPU 0 runs user tasks unless you
> forces these otherwise.
Thanks. I'll put it down to a bad .config choice, although it was
fine on early 4.1. While I was starting to bisect, I noticed that
on the A10 everything was happening on CPU 0 - not sure if that was
happening on the original box, but for the moment it sounds likely.
ĸen
--
This one goes up to eleven!
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