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

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Message-ID: <4CE4C091.8060306@hitachi.com>
Date:	Thu, 18 Nov 2010 14:58:41 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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>,
	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 3:23), Mathieu Desnoyers wrote:
> Amongst others, Ericsson rely on this kind of feature. The case where we're
> filtering "out" should be really, really fast (even if it makes the recording
> slightly slower). If there is a race modifying the data underneath between the
> filter execution and the copy to the buffers, I really don't think it matters.
> If the tracepoint caller context don't provide data consistency guarantees for
> the parameters it passes, we should not expect 100% perfect consistency between
> filter and what is actually saved in the trace. The trace analysis tools should
> just be able to cope with that, but I really don't think anyone should care.
> 
> So I would recommend no copy, filter directly on the source data, stop the
> filter chain as soon as a non-match is observed. Copy the data into the buffers
> if the filter passes.

Indeed, so that we can eliminate memory write accesses. :)

Thanks,

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