Return-path: Received: from smtp-out-068.synserver.de ([212.40.180.68]:1062 "HELO smtp-out-068.synserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1760247AbZJIDvz (ORCPT ); Thu, 8 Oct 2009 23:51:55 -0400 Date: Fri, 9 Oct 2009 05:51:17 +0200 From: Markus Trippelsdorf To: Mike Galbraith Cc: Frans Pop , Arjan van de Ven , Linux Kernel Mailing List , Ingo Molnar , Peter Zijlstra , linux-wireless@vger.kernel.org Subject: Re: [.32-rc3] scheduler: iwlagn consistently high in "waiting for CPU" Message-ID: <20091009035117.GB1985@phenom2.trippelsdorf.de> References: <200910051500.55875.elendil@planet.nl> <1254974743.7797.21.camel@marge.simson.net> <20091008064041.67219b13@infradead.org> <200910081655.37485.elendil@planet.nl> <1255026217.6643.12.camel@marge.simson.net> <20091008203426.GA1946@phenom2.trippelsdorf.de> <1255059318.7236.13.camel@marge.simson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1255059318.7236.13.camel@marge.simson.net> Sender: linux-wireless-owner@vger.kernel.org List-ID: On Fri, Oct 09, 2009 at 05:35:18AM +0200, Mike Galbraith wrote: > On Thu, 2009-10-08 at 22:34 +0200, Markus Trippelsdorf wrote: > > On Thu, Oct 08, 2009 at 08:23:37PM +0200, Mike Galbraith wrote: > > > On Thu, 2009-10-08 at 16:55 +0200, Frans Pop wrote: > > > > On Thursday 08 October 2009, Arjan van de Ven wrote: > > > > > From: Arjan van de Ven > > > > > Date: Thu, 24 Sep 2009 13:24:16 +0200 > > > > > Subject: [PATCH] x86, timers: check for pending timers after (device) > > > > > interrupts > > > > > > > > > > Now that range timers and deferred timers are common, I found a > > > > > problem with these using the "perf timechart" tool. > > > > > > > > > > It turns out that on x86, these two 'opportunistic' timers only > > > > > get checked when another "real" timer happens. > > > > > These opportunistic timers have the objective to save power by > > > > > hitchhiking on other wakeups, as to avoid CPU wakeups by themselves > > > > > as much as possible. > > > > > > > > This patch makes quite a difference for me. iwlagn and phy0 now > > > > consistently show at ~10 ms or lower. > > > > > > > > I do still get occasional high latencies, but those are for things like > > > > "[rpc_wait_bit_killable]" or "Writing a page to disk", where I guess you'd > > > > expect them. Those high latencies are mostly only listed for "Global" and > > > > don't translate to individual processes. > > > > > > I still see very high latencies coming out of idle (last noted was > > > > 300ms, NO_HZ) with this patch, and wonder if the hunk below makes any > > > difference whatsoever for you. Here, it definitely does. (shouldn't) > > > > I'm also seeing these strange, very high latencies here. Your patch > > didn't help unfortunately. > > > > This is from an otherwise idle NO_NZ system: > > > > # ./perf sched latency > > > > ----------------------------------------------------------------------------------------- > > Task | Runtime ms | Switches | Average delay ms | Maximum delay ms | > > ----------------------------------------------------------------------------------------- > > ksoftirqd/0:4 | 2.216 ms | 170 | avg: 24.235 ms | max: 808.356 ms | > > ksoftirqd/1:6 | 2.611 ms | 205 | avg: 4.334 ms | max: 165.553 ms | > > migration/2:7 | 0.000 ms | 1 | avg: 3.060 ms | max: 3.060 ms | > > > > With latencytop the ksoftirqd latency is over 1 sec frequently. (Could be > > ondemand CPUfreq governor related?) > > That's a separate issue, which Arjan was nice enough to fix for me. He > even wrote the changelog, and used my mouse to do so ;-) > > > Repeatable. Apply patchlet, and the numbers below become repeatable. > > perf_counter tools: make perf sched pass -F 0 to record > > Commit 42e59d7d19dc4b4 introduced a sample frequency framework.. > .. however it unfortunately changed how perf events get recorded, > and caused sched to miss events. > > This patch causes the sched code to use -F 0 to not use the > new framework when recording sched data. Yes, your're right. With this patch applied perf sched latency is back to normal. -- Markus