linux-kernel - Re: Multiple Tracers

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Message-ID: <20090409025507.GB24946@ghostprotocols.net>
Date:	Wed, 8 Apr 2009 23:55:07 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	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
Subject: Re: Multiple Tracers

Em Thu, Apr 09, 2009 at 10:11:48AM +0800, Li Zefan escreveu:
> 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> ;)

Nope, Tom:

Message-Id: <1235725261.8512.89.camel@...rm-linux>
 
> > 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.

Yeah, being able to mix all kinds of tracers is the way to go.

- Arnaldo
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