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SubjectRe: Multiple Tracers

* Steven Whitehouse <swhiteho@redhat.com> wrote:

> Hi,
>
> On Wed, 2009-04-08 at 15:53 +0200, Ingo Molnar wrote:
> > * 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
>
> 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
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.

Ingo


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