[RFC][PATCH 8/9] perf: Change close() semantics for group events

From: Peter Zijlstra
Date: Sat Apr 09 2011 - 15:23:46 EST

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@xxxxxxxxx>
kernel/perf_event.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)

Index: linux-2.6/kernel/perf_event.c
--- linux-2.6.orig/kernel/perf_event.c
+++ linux-2.6/kernel/perf_event.c
@@ -2920,12 +2920,6 @@ int perf_event_release_kernel(struct per
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);
* There are two ways this annotation is useful:
@@ -2942,8 +2936,8 @@ int perf_event_release_kernel(struct per
mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
- list_del_event(event, ctx);
+ perf_remove_from_context(event);


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