Date: Wed, 8 Apr 2009 15:53:12 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Steven Whitehouse <swhiteho@redhat.com>
Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org, mingo@redhat.com,
       axboe@kernel.dk
Subject: Re: Multiple Tracers
Message-ID: <20090408135312.GR18581@elte.hu>
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* Steven Whitehouse <swhiteho@redhat.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
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