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perf_counter: optimize perf_counter_task_tick() 

perf_counter_task_tick() does way too much work to find out
there's nothing to do. Provide an easy short-circuit for the
normal case where there are no counters on the system.

[ Impact: micro-optimization ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090508170028.750619201@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-05-08 18:52:21 +02:00 committed by Ingo Molnar
parent 3611dfb8ed
commit 7fc23a5380
1 changed files with 11 additions and 2 deletions
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13
kernel/perf_counter.c
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@ -39,6 +39,7 @@ int perf_max_counters __read_mostly = 1;
static int perf_reserved_percpu __read_mostly;
static int perf_overcommit __read_mostly = 1;
static atomic_t nr_counters __read_mostly;
static atomic_t nr_mmap_tracking __read_mostly;
static atomic_t nr_munmap_tracking __read_mostly;
static atomic_t nr_comm_tracking __read_mostly;
@ -1076,8 +1077,14 @@ static void rotate_ctx(struct perf_counter_context *ctx)
void perf_counter_task_tick(struct task_struct *curr, int cpu)
{
struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
struct perf_counter_context *ctx = &curr->perf_counter_ctx;
struct perf_cpu_context *cpuctx;
struct perf_counter_context *ctx;
if (!atomic_read(&nr_counters))
return;
cpuctx = &per_cpu(perf_cpu_context, cpu);
ctx = &curr->perf_counter_ctx;
perf_counter_cpu_sched_out(cpuctx);
perf_counter_task_sched_out(curr, cpu);
@ -1197,6 +1204,7 @@ static void free_counter(struct perf_counter *counter)
{
perf_pending_sync(counter);
atomic_dec(&nr_counters);
if (counter->hw_event.mmap)
atomic_dec(&nr_mmap_tracking);
if (counter->hw_event.munmap)
@ -2861,6 +2869,7 @@ done:
counter->pmu = pmu;
atomic_inc(&nr_counters);
if (counter->hw_event.mmap)
atomic_inc(&nr_mmap_tracking);
if (counter->hw_event.munmap)