perf_events: Fix perf buffer watermark setting
authorVince Weaver <vweaver1@eecs.utk.edu>
Wed, 1 Jun 2011 19:15:36 +0000 (15:15 -0400)
committerIngo Molnar <mingo@elte.hu>
Fri, 1 Jul 2011 09:06:32 +0000 (11:06 +0200)
commit4ec8363dfc1451f8c8f86825731fe712798ada02
tree12db5b26a3ffa179ef119ac945c4d9a6fb1ced88
parent0f933625e7b6c3d91878ae95e341bf1984db7eaf
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>
kernel/events/core.c
kernel/events/ring_buffer.c