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    SubjectRe: [PATCH] perf: Don't schedule tracepoints when exclude_kernel is set
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    On Sat, 2011-04-09 at 15:27 +0200, Frederic Weisbecker wrote:
    > On Sat, Apr 09, 2011 at 03:14:44PM +0200, Peter Zijlstra wrote:
    > > On Fri, 2011-04-08 at 22:57 +0200, Frederic Weisbecker wrote:
    > > > Instead of checking attr.exclude_kernel anytime a tracepoint
    > > > event triggers, simply don't schedule the tracepoint it that
    > > > attribute is set. This makes one test less in the tracing
    > > > path.
    > >
    > > Meh, I'd much rather someone spend some time on finishing the below,
    > > which is a much bigger improvement for trace-events.
    >
    > I secretely added that to my pile already :)
    > That's indeed something we really want.
    >
    > The above is just a little thing I noticed yesterday and I wanted
    > to fix. Nothing more.
    >
    > About that tracepoint collection, I'm not sure I like the idr though.
    > That thing seems to be O(log(n)), I which we can rather approach O(1)
    > when possible, using a hlist perhaps.

    We only do 2 idr lookups at most and don't get to muck about with hash
    table collisions etc. But if you can show that that is the bottleneck
    you can replace the task/cpu idrs with a hashtable.

    You will still need an IDR to deal with the traceevents (trace_type_idr)
    in order to get the dense ID space, and the per-event idr isn't used in
    the fast path at all.




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