From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753547AbZBJFwt (ORCPT ); Tue, 10 Feb 2009 00:52:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751165AbZBJFwk (ORCPT ); Tue, 10 Feb 2009 00:52:40 -0500 Received: from mail.gmx.net ([213.165.64.20]:33672 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750920AbZBJFwj (ORCPT ); Tue, 10 Feb 2009 00:52:39 -0500 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX19v3tk1Uz9vBvJGQId3oHE+zKBa0x5vja4P7KpHtG kcUKtRbRJ5M7zY Subject: Re: [PATCH 0/2] fix the itimer regression (BZ 12618) From: Mike Galbraith To: Ingo Molnar Cc: Lin Ming , Peter Zijlstra , "Zhang, Yanmin" , "tglx@linutronix.de" , "oleg@redhat.com" , "linux-kernel@vger.kernel.org" , "seto.hidetoshi@jp.fujitsu.com" In-Reply-To: <20090209214723.GA2664@elte.hu> References: <20090205112414.104100700@chello.nl> <20090205120608.GB8799@elte.hu> <1233895919.2604.323.camel@ymzhang> <20090206151832.GL18368@elte.hu> <1234161961.5991.41.camel@minggr.sh.intel.com> <20090209214723.GA2664@elte.hu> Content-Type: text/plain; charset=utf-8 Date: Tue, 10 Feb 2009 06:52:34 +0100 Message-Id: <1234245154.6033.92.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1.1 Content-Transfer-Encoding: 8bit X-Y-GMX-Trusted: 0 X-FuHaFi: 0.53 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2009-02-09 at 22:47 +0100, Ingo Molnar wrote: > * Lin Ming wrote: > > > On Fri, 2009-02-06 at 23:18 +0800, Ingo Molnar wrote: > > > * Zhang, Yanmin wrote: > > > > > > > On Thu, 2009-02-05 at 13:06 +0100, Ingo Molnar wrote: > > > > > * Peter Zijlstra wrote: > > > > > > > > > > > This should hopefully address all the itimer borkage. > > > > > > > > > > Applied to tip:timers/urgent, thanks Peter! > > > > > > > > > > Yanmin: could you check hacbench_pth with latest tip/master, do > > > > > these fixes resolve that 3% regression you reported? > > > > > > > > Lin Ming tested it and hackbench_pth/volanoMark regression all disappear. > > > > But oltp has a regression. We think oltp new regression isn't related to > > > > the patch. Ming is investigating it. > > > > > > Potential suspects for oltp regression would be: > > > > > > 3d39870: sched_rt: don't use first_cpu on cpumask created with cpumask_and > > > a571bbe: sched: fix buddie group latency > > > a9f3e2b: sched: clear buddies more aggressively > > > 1596e29: sched: symmetric sync vs avg_overlap > > > d942fb6: sched: fix sync wakeups > > > > I tested the latest tip-master branch. > > After reverting "d942fb6: sched: fix sync wakeups", the oltp regression > > on the 8cores Stockley machine is mostly fixed. > > > > On another 4*4 cores Tigerton machine, oltp has more than 10% regression > > with 2.6.29-rc4 compared with 2.6.29-rc3. > > ok, that commit needs fixed or reverted. Peter, Mike? I see some ~problems. Looking at the tasks sitting in my ~idle box right now: tasks 284, avg_overlap = 0.000000 196 starts make -j30 tasks 401, avg_overlap = 0.000000 285 0.0 (should) means zero wakeups since birth, it does not mean this task is showing synchronous behavior until it's non-zero. New tasks start with zero, so until they grow an avg_overlap, when they wake, at least half of the decision making data is bogus/non-existent. With make -j30, I added 117 tasks, 89 are unknown, 28 known. This parallel load _tries_ to go affine. On an nfs mount where runners are also frequent (and truly synchronous) wakers, it tries really hard. IOW, I think the affinity logic may become too strong when strengthened by flipping the hint. I originally inverted that test to filter out the case where we _have_ behavioral data indicating that the tasks in question were definitely not synchronous despite the sync wakeup hint. Another ~problem is that a task with low avg_overlap can change behavior to cpu hog, and retain it's stale avg_overlap up to forever. Maybe we shouldn't use avg_overlap until it's been established. But.. Flip-side: I have a strong feeling that that _not_ using it would have negative impact. Freshly forked task generates red-hot data for a yet to be awakened partner... Sigh. Damned if ya do, damned if ya don't. -Mike