From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752262AbbJCMtH (ORCPT ); Sat, 3 Oct 2015 08:49:07 -0400 Received: from mail-wi0-f178.google.com ([209.85.212.178]:37610 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752132AbbJCMtE (ORCPT ); Sat, 3 Oct 2015 08:49:04 -0400 Message-ID: <1443876541.3901.14.camel@gmail.com> Subject: Re: 4.2.2: NR_CPUS effectively being 1 bug From: Mike Galbraith To: Frederic Weisbecker Cc: Ingo Molnar , Peter Zijlstra , Andrew Morton , Alexey Dobriyan , linux-kernel@vger.kernel.org, Ingo Molnar , Christoph Lameter Date: Sat, 03 Oct 2015 14:49:01 +0200 In-Reply-To: <20151003123115.GA6389@lerouge> References: <20151002204658.GA1970@p183.telecom.by> <20151002140033.ef62cd83936263311eb210d8@linux-foundation.org> <20151003065320.GE3816@twins.programming.kicks-ass.net> <20151003073812.GA24548@gmail.com> <1443860148.3786.5.camel@gmail.com> <20151003081801.GA26114@gmail.com> <1443860671.3786.8.camel@gmail.com> <20151003085232.GA27214@gmail.com> <1443873884.3215.2.camel@gmail.com> <20151003123115.GA6389@lerouge> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2015-10-03 at 14:31 +0200, Frederic Weisbecker wrote: > On Sat, Oct 03, 2015 at 02:04:44PM +0200, Mike Galbraith wrote: > > On Sat, 2015-10-03 at 10:52 +0200, Ingo Molnar wrote: > > > Ok, looks like a patch with good intentions but bad effects. Mind sending a revert > > > patch, changelogged, signed off? > > > > No. They know. > > The reason for this patch is that NO_HZ_FULL is only useful on a CPU if no task > other than the desired one can be scheduled on it. Hence the cpu_isolated_map. Yes, but makes it needlessly static. > Only those who enable NO_HZ_FULL_ALL by accident do complain, not those who > really use it so far. At least it makes people realize their mistake. > > That said I never liked that cpu_isolated_map. And some regular non-isolation > work may be needed to be done even on NO_HZ_FULL_ALL machines and it that > case we get screwed. ATM, using nohz_full CPUs for generic work has a high price, but those CPUs work just fine. Andy is allegedly gonna make that overhead go away, at which time dynamic sets become a much more attractive, but you can do that now. > So I should revert that and defer that isolation work to explicit affinity > setting or cpusets. Yay. -Mike