perf: Optimize perf_event_task_ctx()
Remove a rcu_read_{,un}lock() pair and a few conditionals.
We can remove the rcu_read_lock() by increasing the scope of one
in the calling function.
We can do away with the system_state check if the machine still
boots after this patch (seems to be the case).
We can do away with the list_empty() check because the bare
list_for_each_entry_rcu() reduces to that now that we've removed
everything else.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091120212508.452227115@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index cda17ac..2afb305 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3267,15 +3267,10 @@
{
struct perf_event *event;
- if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
- return;
-
- rcu_read_lock();
list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
if (perf_event_task_match(event))
perf_event_task_output(event, task_event);
}
- rcu_read_unlock();
}
static void perf_event_task_event(struct perf_task_event *task_event)
@@ -3283,11 +3278,11 @@
struct perf_cpu_context *cpuctx;
struct perf_event_context *ctx = task_event->task_ctx;
+ rcu_read_lock();
cpuctx = &get_cpu_var(perf_cpu_context);
perf_event_task_ctx(&cpuctx->ctx, task_event);
put_cpu_var(perf_cpu_context);
- rcu_read_lock();
if (!ctx)
ctx = rcu_dereference(task_event->task->perf_event_ctxp);
if (ctx)