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authorVince Weaver <vweaver1@eecs.utk.edu>2011-06-01 15:15:36 -0400
committerIngo Molnar <mingo@elte.hu>2011-07-01 11:06:32 +0200
commit4ec8363dfc1451f8c8f86825731fe712798ada02 (patch)
tree12db5b26a3ffa179ef119ac945c4d9a6fb1ced88 /kernel/events
parent0f933625e7b6c3d91878ae95e341bf1984db7eaf (diff)
downloadlwn-4ec8363dfc1451f8c8f86825731fe712798ada02.tar.gz
lwn-4ec8363dfc1451f8c8f86825731fe712798ada02.zip
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 <vweaver1@eecs.utk.edu> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <stable@kernel.org> Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1106011506390.5384@cl320.eecs.utk.edu Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/events')
-rw-r--r--kernel/events/core.c6
-rw-r--r--kernel/events/ring_buffer.c16
2 files changed, 13 insertions, 9 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 && wakeup_events) {
- int events = local_inc_return(&rb->events);
- if (events >= wakeup_events) {
- local_sub(wakeup_events, &rb->events);
- local_inc(&rb->wakeup);
+ if (handle->sample && !event->attr.watermark) {
+ int wakeup_events = event->attr.wakeup_events;
+
+ if (wakeup_events) {
+ int events = local_inc_return(&rb->events);
+ if (events >= wakeup_events) {
+ local_sub(wakeup_events, &rb->events);
+ local_inc(&rb->wakeup);
+ }
}
}