Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757586Ab3GWMpk (ORCPT ); Tue, 23 Jul 2013 08:45:40 -0400 Received: from merlin.infradead.org ([205.233.59.134]:40849 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757438Ab3GWMpi (ORCPT ); Tue, 23 Jul 2013 08:45:38 -0400 Date: Tue, 23 Jul 2013 14:45:25 +0200 From: Peter Zijlstra To: Don Zickus Cc: Frederic Weisbecker , LKML , Jiri Olsa , Namhyung Kim , Ingo Molnar , Arnaldo Carvalho de Melo , Stephane Eranian , "Srivatsa S. Bhat" , Anish Singh Subject: Re: [PATCH 8/8] watchdog: Remove hack to make full dynticks working Message-ID: <20130723124525.GA27075@twins.programming.kicks-ass.net> References: <1374539466-4799-1-git-send-email-fweisbec@gmail.com> <1374539466-4799-9-git-send-email-fweisbec@gmail.com> <20130723123331.GE126784@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130723123331.GE126784@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1340 Lines: 28 On Tue, Jul 23, 2013 at 08:33:31AM -0400, Don Zickus wrote: > On Tue, Jul 23, 2013 at 02:31:06AM +0200, Frederic Weisbecker wrote: > > A perf event can be used without forcing the tick to > > stay alive if it doesn't use a frequency but a sample > > period and if it doesn't throttle (raise storm of events). > > > > Since the lockup detector neither use a perf event frequency > > nor should ever throttle due to its high period, it can now > > run concurrently with the full dynticks feature. > > Thanks. Dumb question, I keep wondering if the lockup detector would be > better or worse off if it used the perf event frequency as opposed to > using a sample period? The idea is it could follow the varying cpu > frequencies better (and probably simplify some of the code too). Right, trouble is that someone didn't consider fractional frequencies when writing the interface :/ Lowest we can go is 1 Hz while we'd want something like 0.1 Hz or smaller. Also, like the above says, that would interfere with the nohz efforts as perf needs the tick to re-compute those frequency thingies. -- 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/