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perf: Optimize perf_event_mmap_ctx()

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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: <20091120212508.606459548@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-11-20 22:19:48 +01:00 committed by Ingo Molnar
parent f6595f3a96
commit f6d9dd237d
1 changed files with 1 additions and 6 deletions
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7
kernel/perf_event.c
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@ -3493,15 +3493,10 @@ static void perf_event_mmap_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_mmap_match(event, mmap_event))
perf_event_mmap_output(event, mmap_event);
}
rcu_read_unlock();
}
static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
@ -3557,11 +3552,11 @@ got_name:
mmap_event->event_id.header.size = sizeof(mmap_event->event_id) + size;
rcu_read_lock();
cpuctx = &get_cpu_var(perf_cpu_context);
perf_event_mmap_ctx(&cpuctx->ctx, mmap_event);
put_cpu_var(perf_cpu_context);
rcu_read_lock();
/*
* doesn't really matter which of the child contexts the
* events ends up in.