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    SubjectRe: [RFC PATCH] tracing: Don't call wakeup() when committing the event
    On Tue, May 3, 2011 at 4:08 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
    > On Tue, May 03, 2011 at 06:47:32PM -0400, Steven Rostedt wrote:
    >> On Wed, 2011-05-04 at 00:09 +0200, Frederic Weisbecker wrote:
    >>
    >> > I wonder if we should have a lite version of wake_up() that checks
    >> > if the list of waiters is empty before locking the queue.
    >> > After all we don't care much about tight races for tracing.
    >>
    >> Since tracing is a special case here, we probably could get away to just
    >> do it ourselves. That is, have our own flag that determines if we should
    >> wakeup or not.
    >
    > Yep, agreed.
    >
    How about this? Check if the waitqueue is active and if true, operate on the
    trace_wait queue.

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 06f4458..e03ee24 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -353,7 +353,7 @@ void trace_wake_up(void)
    {
    int cpu;

    - if (trace_flags & TRACE_ITER_BLOCK)
    + if (trace_flags & TRACE_ITER_BLOCK || !waitqueue_active(&trace_wait))
    return;
    /*
    * The runqueue_is_locked() can fail, but this is the best we
    Vaibhav Nagarnaik


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