perf: Optimize ctx_sched_out()

    Oleg noted that ctx_sched_out() disables the PMU even though it might
    not actually do something, avoid needless PMU-disabling.

    Reported-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/20110409192141.665385503@chello.nl
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
perf: Clean up 'ctx' reference counting

    Small cleanup to how we refcount in find_get_context(), this also
    allows us to use put_ctx() to free things instead of using kfree().

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/20110409192141.719340481@chello.nl
    Signed-off-by: Ingo Molnar <mingo@elte.hu>