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easily on any system post SNB (which do not publish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>

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index e7e63a91ec05aee62a307cc5999d628f9e10ba36..1b443db2db5005d62ed4e08f918fdfcaa071ac37 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1534,6 +1534,7 @@ static void __init filter_events(struct attribute **attrs)
 {
        struct device_attribute *d;
        struct perf_pmu_events_attr *pmu_attr;
+       int offset = 0;
        int i, j;
 
        for (i = 0; attrs[i]; i++) {
@@ -1542,7 +1543,7 @@ static void __init filter_events(struct attribute **attrs)
                /* 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++)
@@ -1550,6 +1551,14 @@ static void __init filter_events(struct attribute **attrs)
 
                /* 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++;
        }
 }