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From: Andrew Vagin <avagin@gmail.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Andrew Vagin <avagin@openvz.org>,
	linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>, Paul Mackerras <paulus@samba.org>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
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.5010006@gmail.com> (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.

  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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