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Subject[tip:perf/core] perf: Optimize perf_event_comm_ctx()
Commit-ID:  f6595f3a9680c86b6332f881a7ae2cbbcfdc8619
Gitweb: http://git.kernel.org/tip/f6595f3a9680c86b6332f881a7ae2cbbcfdc8619
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 20 Nov 2009 22:19:47 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 21 Nov 2009 14:11:36 +0100

perf: Optimize perf_event_comm_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: <20091120212508.527608793@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
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 2afb305..4deefaa 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3374,15 +3374,10 @@ static void perf_event_comm_ctx(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_event_comm_match(event))
perf_event_comm_output(event, comm_event);
}
- rcu_read_unlock();
}

static void perf_event_comm_event(struct perf_comm_event *comm_event)
@@ -3401,11 +3396,11 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)

comm_event->event_id.header.size = sizeof(comm_event->event_id) + size;

+ rcu_read_lock();
cpuctx = &get_cpu_var(perf_cpu_context);
perf_event_comm_ctx(&cpuctx->ctx, comm_event);
put_cpu_var(perf_cpu_context);

- rcu_read_lock();
/*
* doesn't really matter which of the child contexts the
* events ends up in.

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