From 4ec8363dfc1451f8c8f86825731fe712798ada02 Mon Sep 17 00:00:00 2001 From: Vince Weaver Date: Wed, 1 Jun 2011 15:15:36 -0400 Subject: [PATCH] perf_events: Fix perf buffer watermark setting Since 2.6.36 (specifically commit d57e34fdd60b ("perf: Simplify the ring-buffer logic: make perf_buffer_alloc() do everything needed"), the perf_buffer_init_code() has been mis-setting the buffer watermark if perf_event_attr.wakeup_events has a non-zero value. This is because perf_event_attr.wakeup_events is a union with perf_event_attr.wakeup_watermark. This commit re-enables the check for perf_event_attr.watermark being set before continuing with setting a non-default watermark. This bug is most noticable when you are trying to use PERF_IOC_REFRESH with a value larger than one and perf_event_attr.wakeup_events is set to one. In this case the buffer watermark will be set to 1 and you will get extraneous POLL_IN overflows rather than POLL_HUP as expected. [ avoid using attr.wakeup_events when attr.watermark is set ] Signed-off-by: Vince Weaver Signed-off-by: Peter Zijlstra Cc: Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1106011506390.5384@cl320.eecs.utk.edu Signed-off-by: Ingo Molnar --- kernel/events/core.c | 6 ++++-- kernel/events/ring_buffer.c | 14 ++++++++------ 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 5e70f62752a2..e4aee519572d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3569,8 +3569,10 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) if (vma->vm_flags & VM_WRITE) flags |= RING_BUFFER_WRITABLE; - rb = rb_alloc(nr_pages, event->attr.wakeup_watermark, - event->cpu, flags); + rb = rb_alloc(nr_pages, + event->attr.watermark ? event->attr.wakeup_watermark : 0, + event->cpu, flags); + if (!rb) { ret = -ENOMEM; goto unlock; diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index fde52595d8f7..fc2701c99207 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -199,13 +199,15 @@ void perf_output_end(struct perf_output_handle *handle) struct perf_event *event = handle->event; struct ring_buffer *rb = handle->rb; - int wakeup_events = event->attr.wakeup_events; + if (handle->sample && !event->attr.watermark) { + int wakeup_events = event->attr.wakeup_events; - if (handle->sample && wakeup_events) { - int events = local_inc_return(&rb->events); - if (events >= wakeup_events) { - local_sub(wakeup_events, &rb->events); - local_inc(&rb->wakeup); + if (wakeup_events) { + int events = local_inc_return(&rb->events); + if (events >= wakeup_events) { + local_sub(wakeup_events, &rb->events); + local_inc(&rb->wakeup); + } } }