From: Andrew Vagin <email@example.com> To: Frederic Weisbecker <firstname.lastname@example.org> Cc: Peter Zijlstra <email@example.com>, Andrew Vagin <firstname.lastname@example.org>, email@example.com, Steven Rostedt <firstname.lastname@example.org>, Ingo Molnar <email@example.com>, Paul Mackerras <firstname.lastname@example.org>, Arnaldo Carvalho de Melo <email@example.com> Subject: Re: [PATCH 3/4] trace: add ability to collect call chain of non-current task. Date: Wed, 28 Sep 2011 17:53:02 +0400 [thread overview] Message-ID: <4E8326BE.firstname.lastname@example.org> (raw) In-Reply-To: <20110927205548.GN18553@somewhere> On 09/28/2011 12:55 AM, Frederic Weisbecker wrote: > On Tue, Sep 27, 2011 at 04:05:51PM +0200, Peter Zijlstra wrote: >> On Mon, 2011-09-26 at 19:55 +0400, Andrew Vagin wrote: >>> Know issues: >>> * Now call chains for non-current tasks are collected on x86 only, >>> but it may be done for other architectures simply. >>> * It collects only kernel call chains, because we can't get direct >>> access to memory of other processes and this operation should be >>> fast enough. >> Also, it changes the semantics of tracepoint, normally you return the >> callchain leading to the tracepoint, this changes that. >> >> >> I'm not entirely against it, as I can see the use, but I would like to >> solicit other opinions. > There is also a problem in perf tools because we are dealing with a > callchain that doesn't belong to the current thread memory mapping and symbol > space. I believe that's a problem once we deal with the userspace part of > the callchain. > > That and the fact there are other ways to get that callchain like taking > the one of the last sched_switch event from the waked thread. > > Perhaps we should use the sched_switch event and a post_sched_switch > event, compute the time difference as a weight and use the callchain of any of > those. Perhaps as a plugin in perf report? > > In any case that rather sounds like something that should be done in post-processing > in userspace, in perf tools. > > We should probably avoid the remote callchains, sounds like asking for complications > everywhere. Thank you for comments and suggestions. I take timeout to think over them.
next prev parent reply other threads:[~2011-09-28 13:53 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-09-26 15:55 [PATCH 0/4] trace: add ability to collect call chains " Andrew Vagin 2011-09-26 15:55 ` [PATCH 1/4] perf: fix counter of ftrace events Andrew Vagin 2011-10-14 19:11 ` Arun Sharma 2011-09-26 15:55 ` [PATCH 2/4] trace: prepare to collect call chains of non-current task Andrew Vagin 2011-09-27 14:02 ` Peter Zijlstra 2011-10-14 19:12 ` Arun Sharma 2011-09-26 15:55 ` [PATCH 3/4] trace: add ability to collect call chain " Andrew Vagin 2011-09-27 14:05 ` Peter Zijlstra 2011-09-27 20:55 ` Frederic Weisbecker 2011-09-28 13:53 ` Andrew Vagin [this message] 2011-12-08 2:02 ` Arun Sharma 2011-12-09 11:07 ` Andrey Vagin 2011-12-14 20:14 ` Arun Sharma 2011-12-15 15:19 ` Andrew Vagin 2011-12-15 19:08 ` Arun Sharma 2011-12-16 0:15 ` Arun Sharma 2011-09-26 15:55 ` [PATCH 4/4] events: sched_stat_template saves call chains of a target task Andrew Vagin
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