[tip:perfcounters/core] perf_counter: Simplify and fix task migration counting

tip-bot for Peter Zijlstra
2009-06-19T11:54:48Z

Commit-ID: e5289d4a181fb6c0b7a7607649af2ffdc491335c
Gitweb: http://git.kernel.org/tip/e5289d4a181fb6c0b7a7607649af2ffdc491335c
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 19 Jun 2009 13:22:51 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 19 Jun 2009 13:43:12 +0200

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>

---
include/linux/perf_counter.h | 4 ----
kernel/perf_counter.c | 23 +----------------------
kernel/sched.c | 3 ++-
3 files changed, 3 insertions(+), 27 deletions(-)

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index e7e7e02..89698d8 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -682,8 +682,6 @@ static inline void perf_counter_mmap(struct vm_area_struct *vma)
extern void perf_counter_comm(struct task_struct *tsk);
extern void perf_counter_fork(struct task_struct *tsk);

-extern void perf_counter_task_migration(struct task_struct *task, int cpu);
-
extern struct perf_callchain_entry *perf_callchain(struct pt_regs *regs);

extern int sysctl_perf_counter_paranoid;
@@ -724,8 +722,6 @@ static inline void perf_counter_mmap(struct vm_area_struct *vma) { }
static inline void perf_counter_comm(struct task_struct *tsk) { }
static inline void perf_counter_fork(struct task_struct *tsk) { }
static inline void perf_counter_init(void) { }
-static inline void perf_counter_task_migration(struct task_struct *task,
- int cpu) { }
#endif

#endif /* __KERNEL__ */
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 7e9108e..8d4f0dd 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -124,7 +124,7 @@ void perf_enable(void)

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 @@ static const struct pmu perf_ops_task_clock = {
.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 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
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;