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 <arjan@xxxxxxxxxxxxxxx> > > > > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
