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>

3 files changed, 55 insertions, 4 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 3078e23c91eb..5e970c7d3fd5 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -179,8 +179,9 @@ struct perf_counter_attr {
                                 comm           :  1, /* include comm data     */
                                 freq           :  1, /* use freq, not period  */
                                 inherit_stat   :  1, /* per task counts       */
+                                enable_on_exec :  1, /* next exec enables     */
 
-                                __reserved_1   : 52;
+                                __reserved_1   : 51;
 
         __u32                   wakeup_events;  /* wakeup every n events */
         __u32                   __reserved_2;
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;
 
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 201ef2367dcb..2e03524a1de0 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -116,8 +116,9 @@ static void create_perf_stat_counter(int counter, int pid)
                                         fd[cpu][counter], strerror(errno));
                 }
         } else {
-                attr->inherit   = inherit;
-                attr->disabled  = 1;
+                attr->inherit        = inherit;
+                attr->disabled       = 1;
+                attr->enable_on_exec = 1;
 
                 fd[0][counter] = sys_perf_counter_open(attr, pid, -1, -1, 0);
                 if (fd[0][counter] < 0 && verbose)
@@ -262,7 +263,6 @@ static int run_perf_stat(int argc, const char **argv)
          * Enable counters and exec the command:
          */
         t0 = rdclock();
-        prctl(PR_TASK_PERF_COUNTERS_ENABLE);
 
         close(go_pipe[1]);
         wait(&status);