perf: Change close() semantics for group events

In order to always call list_del_event() on the correct cpu if the
event is part of an active context and avoid having to do two IPIs,
change the close() semantics slightly.

The current perf_event_disable() call would disable a whole group if
the event that's being closed is the group leader, whereas the new
code keeps the group siblings enabled.

People should not rely on this behaviour and I don't think they do,
but in case we find they do, the fix is easy and we have to take the
double IPI cost.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Vince Weaver <vweaver1@eecs.utk.edu>
Link: http://lkml.kernel.org/r/20110409192142.038377551@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 802f3b24eeefbd9e47a7225eb43bd4cfb2bb3d94..c378062da2772d5007d63d550bb0e83895f31bb9 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2920,12 +2920,6 @@ int perf_event_release_kernel(struct perf_event *event)
 {
        struct perf_event_context *ctx = event->ctx;
 
-       /*
-        * Remove from the PMU, can't get re-enabled since we got
-        * here because the last ref went.
-        */
-       perf_event_disable(event);
-
        WARN_ON_ONCE(ctx->parent_ctx);
        /*
         * There are two ways this annotation is useful:
@@ -2942,8 +2936,8 @@ int perf_event_release_kernel(struct perf_event *event)
        mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
        raw_spin_lock_irq(&ctx->lock);
        perf_group_detach(event);
-       list_del_event(event, ctx);
        raw_spin_unlock_irq(&ctx->lock);
+       perf_remove_from_context(event);
        mutex_unlock(&ctx->mutex);
 
        free_event(event);