perf_counter: Solve the rotate_ctx vs inherit race differently

Instead of disabling RR scheduling of the counters, use a different list
that does not get rotated to iterate the counters on inheritance.

[ Impact: cleanup, 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>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <20090520102553.237504544@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 10 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 4d8f97375f3a..64113e6d1942 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1120,8 +1120,7 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu)
         __perf_counter_task_sched_out(ctx);
 
         rotate_ctx(&cpuctx->ctx);
-        if (ctx->rr_allowed)
-                rotate_ctx(ctx);
+        rotate_ctx(ctx);
 
         perf_counter_cpu_sched_in(cpuctx, cpu);
         perf_counter_task_sched_in(curr, cpu);
@@ -3109,7 +3108,6 @@ __perf_counter_init_context(struct perf_counter_context *ctx,
         mutex_init(&ctx->mutex);
         INIT_LIST_HEAD(&ctx->counter_list);
         INIT_LIST_HEAD(&ctx->event_list);
-        ctx->rr_allowed = 1;
         ctx->task = task;
 }
 
@@ -3350,14 +3348,14 @@ void perf_counter_init_task(struct task_struct *child)
          */
         mutex_lock(&parent_ctx->mutex);
 
-        parent_ctx->rr_allowed = 0;
-        barrier(); /* irqs */
-
         /*
          * We dont have to disable NMIs - we are only looking at
          * the list, not manipulating it:
          */
-        list_for_each_entry(counter, &parent_ctx->counter_list, list_entry) {
+        list_for_each_entry_rcu(counter, &parent_ctx->event_list, event_entry) {
+                if (counter != counter->group_leader)
+                        continue;
+
                 if (!counter->hw_event.inherit)
                         continue;
 
@@ -3366,9 +3364,6 @@ void perf_counter_init_task(struct task_struct *child)
                         break;
         }
 
-        barrier(); /* irqs */
-        parent_ctx->rr_allowed = 1;
-
         mutex_unlock(&parent_ctx->mutex);
 }