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[209.132.180.67]) by mx.google.com with ESMTP id b13-v6si20053028pgg.89.2018.10.18.03.39.11; Thu, 18 Oct 2018 03:39:27 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728103AbeJRSif (ORCPT + 99 others); Thu, 18 Oct 2018 14:38:35 -0400 Received: from mail.sssup.it ([193.205.80.98]:38619 "EHLO mail.santannapisa.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727519AbeJRSif (ORCPT ); Thu, 18 Oct 2018 14:38:35 -0400 Received: from [10.30.3.207] (account l.abeni@santannapisa.it HELO luca64) by santannapisa.it (CommuniGate Pro SMTP 6.1.11) with ESMTPSA id 133796171; Thu, 18 Oct 2018 12:38:10 +0200 Date: Thu, 18 Oct 2018 12:38:05 +0200 From: luca abeni To: Juri Lelli Cc: Peter Zijlstra , Thomas Gleixner , Juri Lelli , syzbot , Borislav Petkov , "H. Peter Anvin" , LKML , mingo@redhat.com, nstange@suse.de, syzkaller-bugs@googlegroups.com, henrik@austad.us, Tommaso Cucinotta , Claudio Scordino , Daniel Bristot de Oliveira Subject: Re: INFO: rcu detected stall in do_idle Message-ID: <20181018123805.0f4cadd0@luca64> In-Reply-To: <20181018101008.GB21611@localhost.localdomain> References: <000000000000a4ee200578172fde@google.com> <20181016140322.GB3121@hirez.programming.kicks-ass.net> <20181016144045.GF9130@localhost.localdomain> <20181016153608.GH9130@localhost.localdomain> <20181018082838.GA21611@localhost.localdomain> <20181018094850.GW3121@hirez.programming.kicks-ass.net> <20181018101008.GB21611@localhost.localdomain> Organization: Scuola Superiore S. Anna X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Juri, On Thu, 18 Oct 2018 12:10:08 +0200 Juri Lelli wrote: [...] > > Yes, a HZ related limit sounds like something we'd want. But if > > we're going to do a minimum sysctl, we should also consider adding > > a maximum, if you set a massive period/deadline, you can, even with > > a relatively low u, incur significant delays. > > > > And do we want to put the limit on runtime or on period ? > > > > That is, something like: > > > > TICK_NSEC/2 < period < 10*TICK_NSEC > > > > and/or > > > > TICK_NSEC/2 < runtime < 10*TICK_NSEC > > > > Hmm, for HZ=1000 that ends up with a max period of 10ms, that's far > > too low, 24Hz needs ~41ms. We can of course also limit the runtime > > by capping u for users (as we should anyway). > > I also thought of TICK_NSEC/2 as a reasonably safe lower limit I tend to think that something larger than "2" should be used (maybe 10? I mean: even if HZ = 100, it might make sense to allow a runtime equal to 1ms...) > that will implicitly limit period as well since > > runtime <= deadline <= period I agree that if we end up with TICK_NSEC/2 for the runtime limit then explicitly enforcing a minimum period is not needed. > Not sure about the upper limit, though. Lower limit is something > related to the inherent granularity of the platform/config, upper > limit is more to do with highest prio stuff with huge period delaying > everything else; doesn't seem to be related to HZ? I agree Luca