[PATCH 1/4] perf_counter: solve the rotate_ctx vs inherit race differently

From: Peter Zijlstra
Date: Wed May 20 2009 - 06:27:37 EST


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

LKML-Reference: <new-submission>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
include/linux/perf_counter.h | 1 -
kernel/perf_counter.c | 15 +++++----------
2 files changed, 5 insertions(+), 11 deletions(-)

Index: linux-2.6/include/linux/perf_counter.h
===================================================================
--- linux-2.6.orig/include/linux/perf_counter.h
+++ linux-2.6/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;

/*
Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -1120,8 +1120,7 @@ void perf_counter_task_tick(struct task_
__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_
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_
*/
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_
break;
}

- barrier(); /* irqs */
- parent_ctx->rr_allowed = 1;
-
mutex_unlock(&parent_ctx->mutex);
}


--

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