1
linux/kernel/events
Eric B Munson 7f310a5d4e perf_event: Fix broken calc_timer_values()
We detected a serious issue with PERF_SAMPLE_READ and
timing information when events were being multiplexing.

Samples would have time_running > time_enabled. That
was easy to reproduce with a libpfm4 example (ran 3
times to cause multiplexing on Core 2):

 $ syst_smpl -e uops_retired:freq=1 &
 $ syst_smpl -e uops_retired:freq=1 &
 $ syst_smpl -e uops_retired:freq=1 &
 IIP:0x0000000040062d ... PERIOD:2355332948 ENA=40144625315 RUN=60014875184
 syst_smpl: WARNING: time_running > time_enabled
	63277537998 uops_retired:freq=1 , scaled

The bug was not present in kernel up to (and including) 3.0. It turns
out the bug was introduced by the following commit:

commit c479429591

    events: Move lockless timer calculation into helper function

The parameters of the function got reversed yet the call sites
were not updated to reflect the change. That lead to time_running
and time_enabled being swapped. That had no effect when there was
no multiplexing because in that case time_running = time_enabled
but it would show up in any other scenario.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110829124112.GA4828@quad
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-08-31 15:56:29 +02:00
..
core.c perf_event: Fix broken calc_timer_values() 2011-08-31 15:56:29 +02:00
hw_breakpoint.c perf: Add context field to perf_event 2011-07-01 11:06:38 +02:00
internal.h perf: Remove the nmi parameter from the swevent and overflow interface 2011-07-01 11:06:35 +02:00
Makefile perf: Split up buffer handling from core code 2011-06-09 12:57:54 +02:00
ring_buffer.c perf: Remove the perf_output_begin(.sample) argument 2011-07-01 11:06:35 +02:00