Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754528AbbFKNOA (ORCPT ); Thu, 11 Jun 2015 09:14:00 -0400 Received: from www.linutronix.de ([62.245.132.108]:56523 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754388AbbFKNNx (ORCPT ); Thu, 11 Jun 2015 09:13:53 -0400 Date: Thu, 11 Jun 2015 15:13:57 +0200 (CEST) From: Thomas Gleixner To: Mike Galbraith cc: LKML , Peter Zijlstra , Ingo Molnar , Steven Rostedt Subject: Re: RFC: futex_wait() can DoS the tick In-Reply-To: <1434022875.4051.5.camel@gmail.com> Message-ID: References: <1433940278.6814.66.camel@gmail.com> <1433957421.6306.28.camel@gmail.com> <1433989634.3411.15.camel@gmail.com> <1434022875.4051.5.camel@gmail.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1346 Lines: 41 On Thu, 11 Jun 2015, Mike Galbraith wrote: > On Thu, 2015-06-11 at 10:34 +0200, Thomas Gleixner wrote: > > > Can you try the following, please? > > > > Enable function tracer and hrtimer events manually. Then watch the irq > > count on cpu3. If it stalls or becomes slow, then stop the trace with > > > > echo 0 >/sys/kernel/debug/tracing/tracing_on > > > > If the overhead of the function tracer hides the problem, then try just > > with hrtimer, sched_switch and irq events. > > Yeah, function tracer hides it. After some fiddling with buffer size to > be able to ever see a tick, I finally have a trace trimmed with a tick > on each end, 175ms gap between them. It's still 1.5 after xz, sending > off list. What you are looking at is the actual timer interrupt vector, but that's not the the tick. # grep 'expire_entry.*tick_sched_timer' trace2 | wc -l 45 175 / 45 =~ 4 . So I you have CPNFIG_HZ=250 The kernel does not care whether the actual interrupt happens or the timer is expired by other means. If Xen relies on the vector, it's none of my problems .... Thanks, tglx -- 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/