linux-kernel - Re: Multiple Tracers

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Date:	Thu, 09 Apr 2009 10:11:48 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Steven Whitehouse <swhiteho@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, axboe@...nel.dk,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: Multiple Tracers

CC: Arnaldo Carvalho de Melo <acme@...hat.com>

Ingo Molnar wrote:
> * Steven Whitehouse <swhiteho@...hat.com> wrote:
> 
>> Hi,
>>
>> On Wed, 2009-04-08 at 15:53 +0200, Ingo Molnar wrote:
>>> * Steven Whitehouse <swhiteho@...hat.com> wrote:
>>>
>>>> Hi,
>>>>
>>>> A little while back I posted a RFC patch which added gfs2 glock 
>>>> tracing to blktrace. There was a suggestion that I should look 
>>>> instead at the generic tracing code and add a new tracer, but I've 
>>>> come up with a couple of issues along the way.
>>>>
>>>> I think from what I can see that its only possible to run a single 
>>>> tracer at once, so running blktrace (for example) would preclude 
>>>> me from also tracing gfs2's glocks at the same time. Also, I can 
>>>> see no mechanism by which I could ensure the sequencing between 
>>>> the blktrace and glock traces other than exporting the blktrace 
>>>> sequence number, even if running multiple tracers at the same time 
>>>> was possible.
>>> There's a recent addition: the EVENT_TRACE() facility. Would that 
>>> suit your purposes?
>>>
>>> 	Ingo
>> If I can get both blktrace and glock trace info from it, then yes. 
>> I thought that the blktrace output went either via the original 
>> relayfs path, or via its own tracer so that it wasn't possible to 
>> use it and the event trace facility at the same time, unless I use 
>> blktrace via relayfs. From what I've read I thought that probably 
>> the relayfs interface for blktrace might eventually be removed in 
>> favour of the generic tracing interface, but I'm not 100% sure of 
>> that, so perhaps someone can confirm the plans in that area?
> 
> Tom Zanussi (Cc:-ed) recently converted the blktrace tracepoints to 

I guess you mean Arnaldo <acme@...hat.com> ;)

> a tracing framework - and i think much of that could be reused to 
> add EVENT_TRACE() tracepoints to blktrace too.
> 
> Tom, what's your take on this?
> 
> In general, this is the direction we want to take: EVENT_TRACE() 
> tracepoints that can be used in a generic way, in any tracer.
> 

Actually we've planed to do this, and for other tracers.

--
Zefan
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