perf_counter: Provide a way to enable counters on exec

This provides a way to mark a counter to be enabled on the next
exec. This is useful for measuring the total activity of a
program without including overhead from the process that
launches it.

This also changes the perf stat command to use this new
facility.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <19017.43927.838745.689203@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 50 insertions, 0 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 66ab1e9d1294..d55a50da2347 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1429,6 +1429,53 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu)
 }
 
 /*
+ * Enable all of a task's counters that have been marked enable-on-exec.
+ * This expects task == current.
+ */
+static void perf_counter_enable_on_exec(struct task_struct *task)
+{
+        struct perf_counter_context *ctx;
+        struct perf_counter *counter;
+        unsigned long flags;
+        int enabled = 0;
+
+        local_irq_save(flags);
+        ctx = task->perf_counter_ctxp;
+        if (!ctx || !ctx->nr_counters)
+                goto out;
+
+        __perf_counter_task_sched_out(ctx);
+
+        spin_lock(&ctx->lock);
+
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                if (!counter->attr.enable_on_exec)
+                        continue;
+                counter->attr.enable_on_exec = 0;
+                if (counter->state >= PERF_COUNTER_STATE_INACTIVE)
+                        continue;
+                counter->state = PERF_COUNTER_STATE_INACTIVE;
+                counter->tstamp_enabled =
+                        ctx->time - counter->total_time_enabled;
+                enabled = 1;
+        }
+
+        /*
+         * Unclone this context if we enabled any counter.
+         */
+        if (enabled && ctx->parent_ctx) {
+                put_ctx(ctx->parent_ctx);
+                ctx->parent_ctx = NULL;
+        }
+
+        spin_unlock(&ctx->lock);
+
+        perf_counter_task_sched_in(task, smp_processor_id());
+ out:
+        local_irq_restore(flags);
+}
+
+/*
  * Cross CPU call to read the hardware counter
  */
 static void __perf_counter_read(void *info)
@@ -2949,6 +2996,9 @@ void perf_counter_comm(struct task_struct *task)
 {
         struct perf_comm_event comm_event;
 
+        if (task->perf_counter_ctxp)
+                perf_counter_enable_on_exec(task);
+
         if (!atomic_read(&nr_comm_counters))
                 return;