linux-kernel - Re: [ANNOUNCE] New utility: 'trace'

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Message-ID: <4CE4C101.9010905@hitachi.com>
Date:	Thu, 18 Nov 2010 15:00:33 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	"Ted Ts'o" <tytso@....edu>, Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Jason Baron <jbaron@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Christoph Hellwig <hch@....de>,
	Pekka Enberg <penberg@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	2nddept-manager@....hitachi.co.jp
Subject: Re: [ANNOUNCE] New utility: 'trace'

(2010/11/18 0:43), Peter Zijlstra wrote:
> On Wed, 2010-11-17 at 10:10 -0500, Steven Rostedt wrote:
>>
>> Right, the problem with filtering is what do we want to filter, and what
>> about copying?
>>
>> Currently, we copy the data into the buffer and then filter on that
>> data. We could also easily filter on the parameters of the tracepoint,
>> but sometimes those parameters do not match the final output (as the
>> case with sched_switch). Do we copy the data into a separate "per cpu"
>> temp buffer, and figure out the filter then? And if the filter is fine,
>> then copy into the buffer. This obviously is slow, due to the multiple
>> copies. We could do this only if the filtering is enabled.
> 
> Right, so what is the primary purpose of this filtering stuff? As it
> stands it makes stuff terribly slow, so you add overhead but the win
> (presumably) is less data output, is that a sane trade-off?
> 
> Most people I've heard -- both at LinuxCon.JP and LPC -- are asking for
> lower overhead tracing (while at the same time demanding more features).

I've also heard a dynamic filtering (or kicking buffer snapshot) request
in LinuxCon.JP. I think filtering is not only for filtering-out purpose,
but also useful for hooking event to take some action. :)

Thank you,


-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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