Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752680Ab0L1Fs2 (ORCPT ); Tue, 28 Dec 2010 00:48:28 -0500 Received: from mailout-de.gmx.net ([213.165.64.22]:43606 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1750739Ab0L1Fs1 (ORCPT ); Tue, 28 Dec 2010 00:48:27 -0500 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1/C9Xo83KLCBV0UDy38Sn+NcGDrsPnaA2lKa8Ykg7 V41NEGk9o3kUuj Subject: Re: [PATCH] sched: Buggy comparison in check_preempt_tick From: Mike Galbraith To: Venkatesh Pallipadi Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Ranjit Manomohan In-Reply-To: <1293348184.6942.72.camel@marge.simson.net> References: <1293236813-31550-1-git-send-email-venki@google.com> <1293263418.6896.54.camel@marge.simson.net> <1293348184.6942.72.camel@marge.simson.net> Content-Type: text/plain; charset="UTF-8" Date: Tue, 28 Dec 2010 06:48:13 +0100 Message-ID: <1293515293.6930.11.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.30.1.2 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1822 Lines: 44 On Sun, 2010-12-26 at 08:23 +0100, Mike Galbraith wrote: > But anyway.. > > echo NO_WAKEUP_PREEMPT > sched_features > echo NO_TESTME > sched_features > two hogs running on isolcpu 3, pid 6890 at nice -2 > > while sleep 1; do grep 'pert.*6890' /proc/sched_debug; done > > runnable tasks: > task PID tree-key switches prio > ------------------------------------------------------- > R pert 6890 50201.071851 7453 118 > R pert 6890 50596.171290 7513 118 +60 > R pert 6890 50991.265264 7572 118 +59 > R pert 6890 51383.781965 7631 118 +59 > pert 6890 51781.463129 7691 118 +60 > > echo TESTME > sched_features > pert 6890 126881.306733 18977 118 > R pert 6890 127273.825719 19036 118 +59 > R pert 6890 127668.928218 19095 118 +59 > R pert 6890 128064.031372 19154 118 +59 > R pert 6890 128459.134339 19213 118 +59 > > ...with a compute load, the thing should be a noop, and appears to be so > (with busted compare fixed anyway;). You have to be well overloaded for > buddies to kick in these days, so it's probably pretty hard to get > enough spread for the thing to fire. I did a bit more testing yesterday with wakeup loads. There's enough spread for the test to nudge things a few [0..4] times per second/core. I'd either fix the comparison, and let it keep on nudging once in a while, or whack the whole thing. -Mike -- 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/