perf_counter: Simplify and fix task migration counting
The task migrations counter was causing rare and hard to decypher
memory corruptions under load. After a day of debugging and bisection
we found that the problem was introduced with:
3f731ca: perf_counter: Fix cpu migration counter
Turning them off fixes the crashes. Incidentally, the whole
perf_counter_task_migration() logic can be done simpler as well,
by injecting a proper sw-counter event.
This cleanup also fixed the crashes. The precise failure mode is
not completely clear yet, but we are clearly not unhappy about
having a fix ;-)
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 7e9108e..8d4f0dd41 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -124,7 +124,7 @@
static void get_ctx(struct perf_counter_context *ctx)
{
- atomic_inc(&ctx->refcount);
+ WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
}
static void free_ctx(struct rcu_head *head)
@@ -3467,27 +3467,6 @@
.read = task_clock_perf_counter_read,
};
-/*
- * Software counter: cpu migrations
- */
-void perf_counter_task_migration(struct task_struct *task, int cpu)
-{
- struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
- struct perf_counter_context *ctx;
-
- perf_swcounter_ctx_event(&cpuctx->ctx, PERF_TYPE_SOFTWARE,
- PERF_COUNT_SW_CPU_MIGRATIONS,
- 1, 1, NULL, 0);
-
- ctx = perf_pin_task_context(task);
- if (ctx) {
- perf_swcounter_ctx_event(ctx, PERF_TYPE_SOFTWARE,
- PERF_COUNT_SW_CPU_MIGRATIONS,
- 1, 1, NULL, 0);
- perf_unpin_context(ctx);
- }
-}
-
#ifdef CONFIG_EVENT_PROFILE
void perf_tpcounter_event(int event_id)
{
diff --git a/kernel/sched.c b/kernel/sched.c
index 8fb88a9..f46540b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1978,7 +1978,8 @@
if (task_hot(p, old_rq->clock, NULL))
schedstat_inc(p, se.nr_forced2_migrations);
#endif
- perf_counter_task_migration(p, new_cpu);
+ perf_swcounter_event(PERF_COUNT_SW_CPU_MIGRATIONS,
+ 1, 1, NULL, 0);
}
p->se.vruntime -= old_cfsrq->min_vruntime -
new_cfsrq->min_vruntime;