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Commit e5289d4a authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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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:

  3f731ca6: 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: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent f5970550

include/linux/perf_counter.h

+0 −4
Original line number Diff line number Diff line
@@ -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__ */

kernel/perf_counter.c

+1 −22
Original line number Diff line number Diff line
@@ -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)

{

kernel/sched.c

+2 −1
Original line number Diff line number Diff line
@@ -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;