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Date: Thu, 26 Jan 2012 03:27:35 +0100 From: Frederic Weisbecker <fweisbec@...il.com> To: Arun Sharma <asharma@...com> Cc: Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org, Arnaldo Carvalho de Melo <acme@...radead.org>, Andrew Vagin <avagin@...nvz.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: [PATCH] trace: reset sleep/block start time on task switch On Wed, Jan 25, 2012 at 02:29:14PM -0800, Arun Sharma wrote: > On 1/25/12 12:15 PM, Steven Rostedt wrote: > > >trace-cmd record -e sched_switch -f 'prev_state == 1 || prev_state == 2' -e sched_stat_sleep sleep 3 > > > >I'm not sure the filter is even needed, and it should still keep up > >fine. > > Better - I didn't see any overruns with trace-cmd. > > Even if we resolve the sampling rate related problems, there is the > issue of: can we trust that a sampled sched_switch event and a > sampled sched_stat_sleep event actually match each other? Well, a sched_stat_sleep event should match the sched_switch with prev as the last targeted task. Or am I missing something? > > There is consensus here that touching an extra cacheline in the > context switch path is a good trade-off given the usefulness of > sleep profiling in troubleshooting latency problems. > > Since it may not be a good trade-off for everyone, we just need to > figure out where to store some per-task state. To recap two > potential paths to investigate: > > * store sleep_start someplace else that no one other than > sched_stat_sleeptime() knows about. > > * store state in task struct that remembers whether the last context > switch was a preemption or not. > > -Arun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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