linux-kernel - Re: Unified tracing buffer

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Date:	Mon, 22 Sep 2008 16:50:16 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Martin Bligh <mbligh@...gle.com>, prasad@...ux.vnet.ibm.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Steven Rostedt <rostedt@...dmis.org>, od@...ell.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, hch@....de,
	David Wilder <dwilder@...ibm.com>, zanussi@...cast.net
Subject: Re: Unified tracing buffer

Peter Zijlstra wrote:
> On Mon, 2008-09-22 at 09:29 -0700, Martin Bligh wrote:
>>>> In conjunction with the previous email on this thread
>>>> (http://lkml.org/lkml/2008/9/22/160), may I suggest
>>>> the equivalent interfaces in -mm tree (2.6.27-rc5-mm1) to be:
>>>>
>>>> relay_printk(<some struct with default filenames/pathnames>, <string>,
>>>> ....) ;
>>>> relay_dump(<some struct with default filenames/pathnames>, <binary
>>>> data>);
>>>> and
>>>> relay_cleanup_all(<the struct name>); - Single interface that cleans up
>>>> all files/directories/output data created under a logical entity.
>>> Dude, relayfs is such a bad performing mess that extending it seems like
>>> a bad idea. Better to write something new and delete everything relayfs
>>> related.
>> There did seem to be pretty universal agreement that we'd rather not
>> use relayfs.
>>
>>> Also, it seems prudent to separate the ring-buffer implementation from
>>> the event encoding/decoding facilities.
>> Right - in conversation I had with Mathieu later, he suggested cleaning up
>> relayfs - I fear this will delay us far too long, and get bogged down.
>> If we can get one clean circular buffer implementation, then both
>> relayfs and the tracing could share that common solution,
> 
> Currently only blktrace and kvmtrace use relayfs, and I've heard people
> talk about converting both to use lttng/ftrace infrastructure. At which
> point relayfs is orphaned and ready for removal.

Hi Peter,
Systemtap is still a heavy user of relayfs. :-)
Anyway, if new buffering mechanism is enough for us, I think
we're happy to move on it.

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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