perf events: Allow per-task-per-cpu counters

In order to allow for per-task-per-cpu counters, useful for
scalability when profiling task hierarchies, we allow installing
events with event->cpu != -1 in task contexts.

__perf_event_sched_in() already skips events where ->cpu
mis-matches the current cpu, fix up __perf_install_in_context()
and __perf_event_enable() to also respect this filter.

This does lead to vary hard to interpret enabled/running times
for such counters, but I don't see a simple solution for that.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: fweisbec@gmail.com
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091216165904.831451147@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -782,6 +782,9 @@ static void __perf_install_in_context(void *info)
 
 	add_event_to_ctx(event, ctx);
 
+	if (event->cpu != -1 && event->cpu != smp_processor_id())
+		goto unlock;
+
 	/*
 	 * Don't put the event on if it is disabled or if
 	 * it is in a group and the group isn't on.
@@ -925,6 +928,9 @@ static void __perf_event_enable(void *info)
 		goto unlock;
 	__perf_event_mark_enabled(event, ctx);
 
+	if (event->cpu != -1 && event->cpu != smp_processor_id())
+		goto unlock;
+
 	/*
 	 * If the event is in a group and isn't the group leader,
 	 * then don't put it on unless the group is on.
@@ -1595,10 +1601,7 @@ static struct perf_event_context *find_get_context(pid_t pid, int cpu)
 	unsigned long flags;
 	int err;
 
-	/*
-	 * If cpu is not a wildcard then this is a percpu event:
-	 */
-	if (cpu != -1) {
+	if (pid == -1 && cpu != -1) {
 		/* Must be root to operate on a CPU event: */
 		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
 			return ERR_PTR(-EACCES);