perf stat: Fix bug in handling events in error state

(This is a patch has been sitting in the Intel CQM/CMT driver series for
 a while, despite not depend on it. Sending it now independently since
 the series is being discarded.)

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>
Reviewed-by: David Carrillo-Cisneros <davidcc@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20170412182301.44406-1-davidcc@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 11 insertions, 5 deletions

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 868e086a6b59..610225b6326e 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -312,8 +312,12 @@ 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)) {
@@ -338,12 +342,14 @@ static int read_counter(struct perf_evsel *counter)
 static void read_counters(void)
 {
         struct perf_evsel *counter;
+        int ret;
 
         evlist__for_each_entry(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);
         }
 }
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 8f5d86bd3501..3779b9f3f134 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1239,7 +1239,7 @@ 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;
@@ -1257,7 +1257,7 @@ 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);