[tip:perf/core] perf: Optimize perf_swevent_ctx_event()

[tip-bot for Peter Zijlstra]

Commit-ID:  81520183878a8813c71c9372de28bb70913ba549
Gitweb:     http://git.kernel.org/tip/81520183878a8813c71c9372de28bb70913ba549
Author:     Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Fri, 20 Nov 2009 22:19:45 +0100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sat, 21 Nov 2009 14:11:35 +0100

perf: Optimize perf_swevent_ctx_event()

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@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
LKML-Reference: <20091120212508.378188589@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/perf_event.c |    7 +------
 1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 8e55b44..cda17ac 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3886,15 +3886,10 @@ static void perf_swevent_ctx_event(struct perf_event_context *ctx,
 {
 	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_swevent_match(event, type, event_id, data, regs))
 			perf_swevent_add(event, nr, nmi, data, regs);
 	}
-	rcu_read_unlock();
 }
 
 static int *perf_swevent_recursion_context(struct perf_cpu_context *cpuctx)
@@ -3926,9 +3921,9 @@ static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
 	(*recursion)++;
 	barrier();
 
+	rcu_read_lock();
 	perf_swevent_ctx_event(&cpuctx->ctx, type, event_id,
 				 nr, nmi, data, regs);
-	rcu_read_lock();
 	/*
 	 * doesn't really matter which of the child contexts the
 	 * events ends up in.
--
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