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    SubjectRe: Multiple Tracers
    Em Thu, Apr 09, 2009 at 10:11:48AM +0800, Li Zefan escreveu:
    > CC: Arnaldo Carvalho de Melo <acme@redhat.com>
    >
    > Ingo Molnar wrote:
    > > * 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
    >
    > I guess you mean Arnaldo <acme@redhat.com> ;)

    Nope, Tom:

    Message-Id: <1235725261.8512.89.camel@charm-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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