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    SubjectRe: [PATCH 03/21] perf_events: Add a helper to search for an event in a context
    On Thu, Jul 01, 2010 at 06:24:24PM +0200, Borislav Petkov wrote:
    > From: Frederic Weisbecker <fweisbec@gmail.com>
    > Date: Thu, Jul 01, 2010 at 12:14:50PM -0400
    >
    > Hi Frederic,
    >
    > > On Thu, Jul 01, 2010 at 06:12:45PM +0200, Peter Zijlstra wrote:
    > > > On Thu, 2010-07-01 at 18:11 +0200, Frederic Weisbecker wrote:
    > > > > I suspect we need another syscall that can list all the persistent events
    > > > > with a unique id and the attrs that follow.
    > > > >
    > > > > So you get a unique id for all of them and you can create an fd on top
    > > > > of this id by using a PERF_FLAG_REQUEST_PERSISTENT and this id put in
    > > > > attr.config.
    > > >
    > > > Isn't that what filesystems were invented for?
    > >
    > >
    > > The problem is when you create a persistent event, you lose the fd.
    > > So you need to retrieve it somehow.
    >
    > actually the idea is to decouple those from the fd alltogether and
    > provide specific file_operations in debugfs and such, as Peter
    > suggested. Which sounds much more sane to me especially since, at least
    > in the MCE case, all the entities that register into that event need to
    > see the same samples (and read the same buffers etc).



    Sure the idea of putting that in fs is better.

    Note the idea of a new syscall was quite close: it would have listed
    unique ids of the persistent events, but not fds, you'd have yet to create
    those fds on top of the ids.



    >
    > And let's try not to read too much into those persistent events - it may
    > just as well be that we need them only for MCEs and nothing else :)


    Not really. It would be useful for boot tracing, amongst various other things
    like flight recorder tracing, etc...



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