Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752398AbbGRN0T (ORCPT ); Sat, 18 Jul 2015 09:26:19 -0400 Received: from mail-wi0-f179.google.com ([209.85.212.179]:35966 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752295AbbGRN0S (ORCPT ); Sat, 18 Jul 2015 09:26:18 -0400 Date: Sat, 18 Jul 2015 15:26:14 +0200 From: Frederic Weisbecker To: Ken Moffat Cc: LKML , Jeff Epler Subject: Re: CONFIG_NO_HZ_FULL restricts cpu usage to the equivalent of one in 4.2 Message-ID: <20150718132613.GD1747@lerouge> References: <20150715162713.GA29360@milliways> <20150716003218.GA15221@milliways> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20150716003218.GA15221@milliways> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1652 Lines: 43 On Thu, Jul 16, 2015 at 01:32:18AM +0100, Ken Moffat wrote: > On Wed, Jul 15, 2015 at 09:11:46PM +0200, Frederic Weisbecker wrote: > > 2015-07-15 18:27 GMT+02:00 Ken Moffat : > > > > > > 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. Yeah we decided to include the nohz_full on cpu_isolated_map recently, except CPU 0. > 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! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/