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>

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 13cb2fb..c8c1dfc 100644 (file)
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -508,7 +508,6 @@ struct perf_counter_context {
        int                     nr_counters;
        int                     nr_active;
        int                     is_active;
-       int                     rr_allowed;
        struct task_struct      *task;
 
        /*

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 4d8f973..64113e6 100644 (file)
--- 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);
 }