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. Signed-off-by: Peter Zijlstra --- kernel/perf_counter.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) Index: linux-2.6/kernel/perf_counter.c =================================================================== --- linux-2.6.orig/kernel/perf_counter.c +++ linux-2.6/kernel/perf_counter.c @@ -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_count 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_cou { 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) -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/