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perf: Optimize perf_swevent_ctx_event()

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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: <20091120212508.378188589@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-11-20 22:19:45 +01:00 committed by Ingo Molnar
parent 0cff784ae4
commit 8152018387
1 changed files with 1 additions and 6 deletions
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7
kernel/perf_event.c
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@ -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.