From: Stephane Eranian eranian@google.com
commit 61b87cae6361ea6af161c1ffa549898892707b19 upstream.
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 This could be verified easily on any system post SNB (which do not publish STALLED_CYCLES_FRONTEND):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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/cpu/perf_event.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -1550,6 +1550,7 @@ static void __init filter_events(struct { struct device_attribute *d; struct perf_pmu_events_attr *pmu_attr; + int offset = 0; int i, j;
for (i = 0; attrs[i]; i++) { @@ -1558,7 +1559,7 @@ static void __init filter_events(struct /* str trumps id */ if (pmu_attr->event_str) continue; - if (x86_pmu.event_map(i)) + if (x86_pmu.event_map(i + offset)) continue;
for (j = i; attrs[j]; j++) @@ -1566,6 +1567,14 @@ static void __init filter_events(struct
/* Check the shifted attr. */ i--; + + /* + * event_map() is index based, the attrs array is organized + * by increasing event index. If we shift the events, then + * we need to compensate for the event_map(), otherwise + * we are looking up the wrong event in the map + */ + offset++; } }