Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751594AbYJaKVy (ORCPT ); Fri, 31 Oct 2008 06:21:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750735AbYJaKVo (ORCPT ); Fri, 31 Oct 2008 06:21:44 -0400 Received: from nebensachen.de ([195.34.83.29]:37870 "EHLO mail.nebensachen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750710AbYJaKVl (ORCPT ); Fri, 31 Oct 2008 06:21:41 -0400 X-Hashcash: 1:20:081031:tytso@mit.edu::IIh6bY1w1FQFPwev:000035tc X-Hashcash: 1:20:081031:linux-kernel@vger.kernel.org::6h5MEeSbPocAq7pI:00000000000000000000000000000000010JQ X-Hashcash: 1:20:081031:tglx@linutronix.de::ejBzGEOyynF0TQun:00000000000000000000000000000000000000000002FsY X-Hashcash: 1:20:081031:mingo@elte.hu::Ulcoz9hVNVu/eY8k:00004XIn From: Elias Oltmanns To: Theodore Tso Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar Subject: Re: [REGRESSION 2.6.28-rc2-git3] lots of extra timer interrupts costing 2W References: <20081031031516.GA9781@mit.edu> Date: Fri, 31 Oct 2008 11:21:34 +0100 In-Reply-To: <20081031031516.GA9781@mit.edu> (Theodore Tso's message of "Thu, 30 Oct 2008 23:15:16 -0400") Message-ID: <87mygl2hg1.fsf@denkblock.local> User-Agent: Gnus/5.110011 (No Gnus v0.11) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2548 Lines: 57 Theodore Tso wrote: > On Wed, Oct 29, 2008 at 10:18:10PM -0400, Theodore Ts'o wrote: >> I've noticed that sometime between 2.6.27-git7 and 2.6.28-rc2-git3, > >> powertop is reporting a huge number of excess timer interrupts on my >> x61s laptop: >> >> Wakeups-from-idle per second : 617.8 interval: 3.1s >> no ACPI power usage estimate available >> >> Top causes for wakeups: >> 71.3% (543.7) : extra timer interrupt >> 13.5% (103.0) : hrtimer_start_expires (tick_sched_timer) >> 7.2% ( 55.0) : Rescheduling interrupts >> 1.7% ( 13.0) gnome-terminal : hrtimer_start_expires (hrtimer_wakeup) >> 1.4% ( 10.3) : PS/2 keyboard/mouse/touchpad >> 1.1% ( 8.3) : ahci >> 0.4% ( 3.3) multiload-apple : hrtimer_start_expires (hrtimer_wakeup) >> 0.3% ( 2.7) Xorg : hrtimer_start (it_real_fn) >> >> >> This is costing me an extra 2 Watts or so. Does this ring a bell with >> anyone, before I start trying to bisect this problem? > > I found the problem via bisection. It's commit fb02fbc1, "NOHZ: > restart tick device from irq_enter()". > > After bisecting the problem, I compiled v2.6.28-rc2 (with the attached > .config file), verified that I saw the extra 500 or so timer > interrupts, and then reverted the commit, and the extra timer > interrupts went away. A more careful measurement of the power drain > difference makes it appear to be more like 0.8 watts. Strange, I can't reproduce this problem here (tested next-20081029 and 2.6.27.4 + some commits including the one in question). However, I'm wondering whether this is simply due to a certain config option since extra timer interrupts doesn't even show up in my powertop output. This is with NO_HZ=y and HIGH_RES_TIMERS=y/n. Could SMP possibly make any difference here? It's disabled in my config. > > This is on an Lenovo X61s laptop. I'm not sure that simply reverting > the commit is the right fix, but it does seem to make the extra timer > interrupts (and the resulting decrease in average C3 residency time) > go away. Well, I'd be rather unhappy, for obvious reasons, if this commit was simply reverted. But, of course, something has got to be done about it. Regards, Elias -- 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/