[PATCH 3/3] perf stat: Remove duplicate event counting

Thomas Richter
2018-06-14T11:49:12Z

Perf stat shows a mismatch in perf stat regarding counter names
on s390:

Run command
[root@s35lp76 perf]# ./perf stat -e tx_nc_tend -v --
~/mytesttx 1 >/tmp/111
tx_nc_tend: 1 573146 573146
tx_nc_tend: 1 573146 573146

Performance counter stats for '/root/mytesttx 1':

3 tx_nc_tend

0.001037252 seconds time elapsed

[root@s35lp76 perf]#

shows transaction counter tx_nc_tend with value 3 but it
was triggered only once as seen by the output of mytesttx.

When looking up the event name tx_nc_tend the following
function sequence is called:

parse_events_multi_pmu_add()
+--> perf_pmu__scan() being called with NULL argument
+--> pmu_read_sysfs() scans directory ../devices/ for
all PMUs
+--> perf_pmu__find() tries to find a PMU in the
global pmu list.
+--> pmu_lookup() called to read all file
entries when not in global
list.

pmu_lookup() causes the issue. It calls
+---> pmu_aliases() to read all the entries in the PMU directory.
On s390 this is named
/sys/devices/cpum_cf/events.
+--> pmu_aliases_parse() reads all files and creates an
alias for each file name.

So we end up with first entry created by
reading the sysfs file
[root@s35lp76 perf]# cat /sys/devices/cpum_cf
/events/TX_NC_TEND
event=0x008d
[root@s35lp76 perf]#

Debug output shows this entry
tx_nc_tend -> 'cpum_cf'/'event=0x008d
'/
After all files in this directory have been
read and aliases created this function is called:
+--> pmu_add_cpu_aliases()
This function looks up the CPU tables
created by the json files.
With json files for s390 now available all
the aliases are added to
the PMU alias list a second time.
The second entry is added by
reading the json file converted by jevent
resulting in file pmu-events/pmu-events.c:

{
.name = "tx_nc_tend",
.event = "event=0x8d",
.desc = "Unit: cpum_cf Completed TEND \
instructions \
in non-constrained TX mode",
.topic = "extended",
.long_desc = "A TEND instruction has \
completed in a \
non-constrained \
transactional-execution mode",
.pmu = "cpum_cf",
},

Debug output shows this entry
tx_nc_tend -> 'cpum_cf'/'event=0x8d'/

Function pmu_aliases_parse() and pmu_add_cpu_aliases()
both use __perf_pmu__new_alias() to add an alias to the
PMU alias list. There is no check if an alias already exist

So we end up with 2 entries for tx_nc_tend in the
PMU alias list.

Having set up the PMU alias list for this PMU now
parse_events_multi_add_pmu() reads the complete alias
list and adds each alias with parse_events_add_pmu()
to the global perfev_list. This causes the alias to
be added multiple times to the event list.

Fix this by making __perf_pmu__new_alias()
to merge alias definitions if an alias is already on the
alias list.
Also print a debug message when the alias has mismatches
in some fields.

Output before:
[root@s35lp76 perf]# ./perf stat -e tx_nc_tend -v \
-- ~/mytesttx 1 >/tmp/111
tx_nc_tend: 1 551446 551446

Performance counter stats for '/root/mytesttx 1':

3 tx_nc_tend

0.000961134 seconds time elapsed

[root@s35lp76 perf]#

Output after:
[root@s35lp76 perf]# ./perf stat -e tx_nc_tend -v \
-- ~/mytesttx 1 >/tmp/111
tx_nc_tend: 1 551446 551446

Performance counter stats for '/root/mytesttx 1':

1 tx_nc_tend

0.000961134 seconds time elapsed

[root@s35lp76 perf]#

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
---
tools/perf/util/pmu.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 70 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index da8f243743d3..a266da1db139 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -234,6 +234,74 @@ static int perf_pmu__parse_snapshot(struct perf_pmu_alias *alias,
return 0;
}

+static void perf_pmu_assign_str(char *name, const char *field, char **old_str,
+ char **new_str)
+{
+ if (!*old_str)
+ goto set_new;
+
+ if (*new_str) { /* Have new string, check with old */
+ if (strcasecmp(*old_str, *new_str))
+ pr_debug("alias %s differs in field '%s'\n",
+ name, field);
+ zfree(old_str);
+ } else /* Nothing new --> keep old string */
+ return;
+set_new:
+ *old_str = *new_str;
+ *new_str = NULL;
+}
+
+static void perf_pmu_update_alias(struct perf_pmu_alias *old,
+ struct perf_pmu_alias *newalias)
+{
+ perf_pmu_assign_str(old->name, "desc", &old->desc, &newalias->desc);
+ perf_pmu_assign_str(old->name, "long_desc", &old->long_desc,
+ &newalias->long_desc);
+ perf_pmu_assign_str(old->name, "topic", &old->topic, &newalias->topic);
+ perf_pmu_assign_str(old->name, "metric_expr", &old->metric_expr,
+ &newalias->metric_expr);
+ perf_pmu_assign_str(old->name, "metric_name", &old->metric_name,
+ &newalias->metric_name);
+ perf_pmu_assign_str(old->name, "value", &old->str, &newalias->str);
+ old->scale = newalias->scale;
+ old->per_pkg = newalias->per_pkg;
+ old->snapshot = newalias->snapshot;
+ memcpy(old->unit, newalias->unit, sizeof(old->unit));
+}
+
+/* Delete an alias entry. */
+static void perf_pmu_free_alias(struct perf_pmu_alias *newalias)
+{
+ zfree(&newalias->name);
+ zfree(&newalias->desc);
+ zfree(&newalias->long_desc);
+ zfree(&newalias->topic);
+ zfree(&newalias->str);
+ zfree(&newalias->metric_expr);
+ zfree(&newalias->metric_name);
+ parse_events_terms__purge(&newalias->terms);
+ free(newalias);
+}
+
+/* Merge an alias, search in alias list. If this name is already
+ * present merge both of them to combine all information.
+ */
+static bool perf_pmu_merge_alias(struct perf_pmu_alias *newalias,
+ struct list_head *alist)
+{
+ struct perf_pmu_alias *a;
+
+ list_for_each_entry(a, alist, list) {
+ if (!strcasecmp(newalias->name, a->name)) {
+ perf_pmu_update_alias(a, newalias);
+ perf_pmu_free_alias(newalias);
+ return true;
+ }
+ }
+ return false;
+}
+
static int __perf_pmu__new_alias(struct list_head *list, char *dir, char *name,
char *desc, char *val,
char *long_desc, char *topic,
@@ -310,7 +378,8 @@ static int __perf_pmu__new_alias(struct list_head *list, char *dir, char *name,
alias->per_pkg = perpkg && sscanf(perpkg, "%d", &num) == 1 && num == 1;
alias->str = strdup(newval);

- list_add_tail(&alias->list, list);
+ if (!perf_pmu_merge_alias(alias, list))
+ list_add_tail(&alias->list, list);

return 0;
}
--
2.14.3