Commit-ID: 4ec8363dfc1451f8c8f86825731fe712798ada02
Gitweb: http://git.kernel.org/tip/4ec8363dfc1451f8c8f86825731fe712798ada02
Author: Vince Weaver <[email protected]>
AuthorDate: Wed, 1 Jun 2011 15:15:36 -0400
Committer: Ingo Molnar <[email protected]>
CommitDate: Fri, 1 Jul 2011 11:06:32 +0200
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 <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: <[email protected]>
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/events/core.c | 6 ++++--
kernel/events/ring_buffer.c | 16 +++++++++-------
2 files changed, 13 insertions(+), 9 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5e70f62..e4aee51 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 fde5259..fc2701c 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);
+ }
}
}
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