diff options
| -rw-r--r-- | include/linux/perf_event.h | 5 | ||||
| -rw-r--r-- | kernel/perf_event.c | 94 |
2 files changed, 30 insertions, 69 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 0b521fc8f5b..f1f853a9d5e 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -597,12 +597,12 @@ struct perf_mmap_data { atomic_t events; /* event_id limit */ atomic_long_t head; /* write position */ - atomic_long_t done_head; /* completed head */ - atomic_t lock; /* concurrent writes */ atomic_t wakeup; /* needs a wakeup */ atomic_t lost; /* nr records lost */ + atomic_t nest; /* nested writers */ + long watermark; /* wakeup watermark */ struct perf_event_mmap_page *user_page; @@ -807,7 +807,6 @@ struct perf_output_handle { unsigned long offset; int nmi; int sample; - int locked; }; #ifdef CONFIG_PERF_EVENTS diff --git a/kernel/perf_event.c b/kernel/perf_event.c index ff5d430d45a..8cf737da3ec 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -2519,8 +2519,6 @@ perf_mmap_data_init(struct perf_event *event, struct perf_mmap_data *data) { long max_size = perf_data_size(data); - atomic_set(&data->lock, -1); - if (event->attr.watermark) { data->watermark = min_t(long, max_size, event->attr.wakeup_watermark); @@ -2906,82 +2904,56 @@ static void perf_output_wakeup(struct perf_output_handle *handle) } /* - * Curious locking construct. - * * We need to ensure a later event_id doesn't publish a head when a former - * event_id isn't done writing. However since we need to deal with NMIs we + * event isn't done writing. However since we need to deal with NMIs we * cannot fully serialize things. * - * What we do is serialize between CPUs so we only have to deal with NMI - * nesting on a single CPU. - * * We only publish the head (and generate a wakeup) when the outer-most - * event_id completes. + * event completes. */ -static void perf_output_lock(struct perf_output_handle *handle) +static void perf_output_get_handle(struct perf_output_handle *handle) { struct perf_mmap_data *data = handle->data; - int cur, cpu = get_cpu(); - handle->locked = 0; - - for (;;) { - cur = atomic_cmpxchg(&data->lock, -1, cpu); - if (cur == -1) { - handle->locked = 1; - break; - } - if (cur == cpu) - break; - - cpu_relax(); - } + preempt_disable(); + atomic_inc(&data->nest); } -static void perf_output_unlock(struct perf_output_handle *handle) +static void perf_output_put_handle(struct perf_output_handle *handle) { struct perf_mmap_data *data = handle->data; unsigned long head; - int cpu; - - data->done_head = data->head; - - if (!handle->locked) - goto out; again: - /* - * The xchg implies a full barrier that ensures all writes are done - * before we publish the new head, matched by a rmb() in userspace when - * reading this position. - */ - while ((head = atomic_long_xchg(&data->done_head, 0))) - data->user_page->data_head = head; + head = atomic_long_read(&data->head); /* - * NMI can happen here, which means we can miss a done_head update. + * IRQ/NMI can happen here, which means we can miss a head update. */ - cpu = atomic_xchg(&data->lock, -1); - WARN_ON_ONCE(cpu != smp_processor_id()); + if (!atomic_dec_and_test(&data->nest)) + return; /* - * Therefore we have to validate we did not indeed do so. + * Publish the known good head. Rely on the full barrier implied + * by atomic_dec_and_test() order the data->head read and this + * write. */ - if (unlikely(atomic_long_read(&data->done_head))) { - /* - * Since we had it locked, we can lock it again. - */ - while (atomic_cmpxchg(&data->lock, -1, cpu) != -1) - cpu_relax(); + data->user_page->data_head = head; + /* + * Now check if we missed an update, rely on the (compiler) + * barrier in atomic_dec_and_test() to re-read data->head. + */ + if (unlikely(head != atomic_long_read(&data->head))) { + atomic_inc(&data->nest); goto again; } if (atomic_xchg(&data->wakeup, 0)) perf_output_wakeup(handle); -out: - put_cpu(); + + preempt_enable(); } void perf_output_copy(struct perf_output_handle *handle, @@ -3063,7 +3035,7 @@ int perf_output_begin(struct perf_output_handle *handle, if (have_lost) size += sizeof(lost_event); - perf_output_lock(handle); + perf_output_get_handle(handle); do { /* @@ -3083,7 +3055,7 @@ int perf_output_begin(struct perf_output_handle *handle, handle->head = head; if (head - tail > data->watermark) - atomic_set(&data->wakeup, 1); + atomic_inc(&data->wakeup); if (have_lost) { lost_event.header.type = PERF_RECORD_LOST; @@ -3099,7 +3071,7 @@ int perf_output_begin(struct perf_output_handle *handle, fail: atomic_inc(&data->lost); - perf_output_unlock(handle); + perf_output_put_handle(handle); out: rcu_read_unlock(); @@ -3117,11 +3089,11 @@ void perf_output_end(struct perf_output_handle *handle) int events = atomic_inc_return(&data->events); if (events >= wakeup_events) { atomic_sub(wakeup_events, &data->events); - atomic_set(&data->wakeup, 1); + atomic_inc(&data->wakeup); } } - perf_output_unlock(handle); + perf_output_put_handle(handle); rcu_read_unlock(); } @@ -3457,22 +3429,13 @@ static void perf_event_task_output(struct perf_event *event, { struct perf_output_handle handle; struct task_struct *task = task_event->task; - unsigned long flags; int size, ret; - /* - * If this CPU attempts to acquire an rq lock held by a CPU spinning - * in perf_output_lock() from interrupt context, it's game over. - */ - local_irq_save(flags); - size = task_event->event_id.header.size; ret = perf_output_begin(&handle, event, size, 0, 0); - if (ret) { - local_irq_restore(flags); + if (ret) return; - } task_event->event_id.pid = perf_event_pid(event, task); task_event->event_id.ppid = perf_event_pid(event, current); @@ -3483,7 +3446,6 @@ static void perf_event_task_output(struct perf_event *event, perf_output_put(&handle, task_event->event_id); perf_output_end(&handle); - local_irq_restore(flags); } static int perf_event_task_match(struct perf_event *event) |