perf/x86: Fix filter_events() bug with event mappings
authorStephane Eranian <eranian@google.com>
Mon, 7 Dec 2015 19:33:25 +0000 (20:33 +0100)
committerIngo Molnar <mingo@kernel.org>
Wed, 6 Jan 2016 10:15:33 +0000 (11:15 +0100)
commit61b87cae6361ea6af161c1ffa549898892707b19
tree638463472954cd1c295b16bf3e08c5f5b30b4e31
parent724697648eec540b2a7561089b1c87cb33e6a0eb
perf/x86: Fix filter_events() bug with event mappings

This patch fixes a bug in the filter_events() function.

The patch fixes the bug whereby if some mappings did not
exist, e.g., STALLED_CYCLES_FRONTEND, then any event after it
in the attrs array would disappear from the published list of
events in /sys/devices/cpu/events. This could be verified
easily on any system post SNB (which do not publish
STALLED_CYCLES_FRONTEND):

$ ./perf stat -e cycles,ref-cycles true
Performance counter stats for 'true':
              1,217,348      cycles
<not supported>      ref-cycles

The problem is that in filter_events() there is an assumption
that the argument (attrs) is organized in increasing continuous
event indexes related to the event_map(). But if we remove the
non-supported events by shifing the position in the array, then
the lookup x86_pmu.event_map() needs to compensate for it, otherwise
we are looking up the wrong index. This patch corrects this problem
by compensating for the deleted events and with that ref-cycles
reappears (here shown on Haswell):

$ perf stat -e ref-cycles,cycles true
Performance counter stats for 'true':
         4,525,910      ref-cycles
         1,064,920      cycles
       0.002943888 seconds time elapsed

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: jolsa@kernel.org
Cc: kan.liang@intel.com
Fixes: 8300daa26755 ("perf/x86: Filter out undefined events from sysfs events attribute")
Link: http://lkml.kernel.org/r/1449516805-6637-1-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/kernel/cpu/perf_event.c