[PATCH v2 31/32] perf/stat: fix bug in handling events in error state

David Carrillo-Cisneros
2016-05-11T23:03:45Z

From: Stephane Eranian <eranian@google.com>

When an event is in error state, read() returns 0
instead of sizeof() buffer. In certain modes, such
as interval printing, ignoring the 0 return value
may cause bogus count deltas to be computed and
thus invalid results printed.

this patch fixes this problem by modifying read_counters()
to mark the event as not scaled (scaled = -1) to force
the printout routine to show <NOT COUNTED>.

Signed-off-by: Stephane Eranian <eranian@google.com>
---
tools/perf/builtin-stat.c | 12 +++++++++---
tools/perf/util/evsel.c | 4 ++--
2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 5645a83..07ef06a 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -289,8 +289,12 @@ static int read_counter(struct perf_evsel *counter)
struct perf_counts_values *count;

count = perf_counts(counter->counts, cpu, thread);
- if (perf_evsel__read(counter, cpu, thread, count))
+ if (perf_evsel__read(counter, cpu, thread, count)) {
+ counter->counts->scaled = -1;
+ perf_counts(counter->counts, cpu, thread)->ena = 0;
+ perf_counts(counter->counts, cpu, thread)->run = 0;
return -1;
+ }

if (STAT_RECORD) {
if (perf_evsel__write_stat_event(counter, cpu, thread, count)) {
@@ -315,12 +319,14 @@ static int read_counter(struct perf_evsel *counter)
static void read_counters(bool close_counters)
{
struct perf_evsel *counter;
+ int ret;

evlist__for_each(evsel_list, counter) {
- if (read_counter(counter))
+ ret = read_counter(counter);
+ if (ret)
pr_debug("failed to read counter %s\n", counter->name);

- if (perf_stat_process_counter(&stat_config, counter))
+ if (ret == 0 && perf_stat_process_counter(&stat_config, counter))
pr_warning("failed to process counter %s\n", counter->name);

if (close_counters) {
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a23f547..57f5fb2 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1150,7 +1150,7 @@ int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
if (FD(evsel, cpu, thread) < 0)
return -EINVAL;

- if (readn(FD(evsel, cpu, thread), count, sizeof(*count)) < 0)
+ if (readn(FD(evsel, cpu, thread), count, sizeof(*count)) <= 0)
return -errno;

return 0;
@@ -1168,7 +1168,7 @@ int __perf_evsel__read_on_cpu(struct perf_evsel *evsel,
if (evsel->counts == NULL && perf_evsel__alloc_counts(evsel, cpu + 1, thread + 1) < 0)
return -ENOMEM;

- if (readn(FD(evsel, cpu, thread), &count, nv * sizeof(u64)) < 0)
+ if (readn(FD(evsel, cpu, thread), &count, nv * sizeof(u64)) <= 0)
return -errno;

perf_evsel__compute_deltas(evsel, cpu, thread, &count);
--
2.8.0.rc3.226.g39d4020