[PATCH v2 05/19] perf, tools: Support weak groups

Andi Kleen
2017-08-11T23:26:44Z

From: Andi Kleen <ak@linux.intel.com>

Setting up groups can be complicated due to the
complicated scheduling restrictions of different PMUs.
User tools usually don't understand all these restrictions.
Still in many cases it is useful to set up groups and
they work most of the time. However if the group
is set up wrong some members will not reported any values
because they never get scheduled.

Add a concept of a 'weak group': try to set up a group,
but if it's not schedulable fallback to not using
a group. That gives us the best of both worlds:
groups if they work, but still a usable fallback if they don't.

In theory it would be possible to have more complex fallback
strategies (e.g. try to split the group in half), but
the simple fallback of not using a group seems to work for now.

So far the weak group is only implemented for perf stat,
not for record.

Here's an unschedulable group (on IvyBridge with SMT on)

% perf stat -e '{branches,branch-misses,l1d.replacement,l2_lines_in.all,l2_rqsts.all_code_rd}' -a sleep 1

73,806,067 branches
4,848,144 branch-misses # 6.57% of all branches
14,754,458 l1d.replacement
24,905,558 l2_lines_in.all
<not supported> l2_rqsts.all_code_rd <------- will never report anything

With the weak group:

% perf stat -e '{branches,branch-misses,l1d.replacement,l2_lines_in.all,l2_rqsts.all_code_rd}:W' -a sleep 1

125,366,055 branches (80.02%)
9,208,402 branch-misses # 7.35% of all branches (80.01%)
24,560,249 l1d.replacement (80.00%)
43,174,971 l2_lines_in.all (80.05%)
31,891,457 l2_rqsts.all_code_rd (79.92%)

The extra event scheduled with some extra multiplexing

v2: Move fallback code to separate function.
Add comment on for_each_group_member
Adjust to new perf_evsel__close interface
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
tools/perf/Documentation/perf-list.txt | 1 +
tools/perf/builtin-stat.c | 35 ++++++++++++++++++++++++++++++++++
tools/perf/util/evsel.h | 1 +
tools/perf/util/parse-events.c | 8 +++++++-
tools/perf/util/parse-events.l | 2 +-
5 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Documentation/perf-list.txt b/tools/perf/Documentation/perf-list.txt
index f709de54707b..d432965d728d 100644
--- a/tools/perf/Documentation/perf-list.txt
+++ b/tools/perf/Documentation/perf-list.txt
@@ -47,6 +47,7 @@ counted. The following modifiers exist:
P - use maximum detected precise level
S - read sample value (PERF_SAMPLE_READ)
D - pin the event to the PMU
+ W - group is weak and will fallback to non-group if not schedulable

The 'p' modifier can be used for specifying how precise the instruction
address should be. The 'p' modifier can be specified multiple times:
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 866da7aa54bf..ac605caf1a01 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -582,6 +582,32 @@ static bool perf_evsel__should_store_id(struct perf_evsel *counter)
return STAT_RECORD || counter->attr.read_format & PERF_FORMAT_ID;
}

+static struct perf_evsel *reset_weak_group(struct perf_evsel *counter)
+{
+ struct perf_evsel *c2, *leader;
+ bool is_open = true;
+
+ leader = counter->leader;
+ pr_debug("Weak group for %s/%d failed\n",
+ leader->name, counter->nr_members);
+
+ /*
+ * for_each_group_member doesn't work here because it doesn't
+ * include the first entry.
+ */
+ evlist__for_each_entry(evsel_list, c2) {
+ if (c2 == counter)
+ is_open = false;
+ if (c2->leader == leader) {
+ if (is_open)
+ perf_evsel__close(c2);
+ c2->leader = c2;
+ c2->nr_members = 0;
+ }
+ }
+ return leader;
+}
+
static int __run_perf_stat(int argc, const char **argv)
{
int interval = stat_config.interval;
@@ -618,6 +644,15 @@ static int __run_perf_stat(int argc, const char **argv)
evlist__for_each_entry(evsel_list, counter) {
try_again:
if (create_perf_stat_counter(counter) < 0) {
+
+ /* Weak group failed. Reset the group. */
+ if (errno == EINVAL &&
+ counter->leader != counter &&
+ counter->weak_group) {
+ counter = reset_weak_group(counter);
+ goto try_again;
+ }
+
/*
* PPC returns ENXIO for HW counters until 2.6.37
* (behavior changed with commit b0a873e).
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 351d3b2d8887..f538c3530227 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -136,6 +136,7 @@ struct perf_evsel {
const char * metric_name;
struct perf_evsel **metric_events;
bool collect_stat;
+ bool weak_group;
};

union u64_swap {
diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 84e301073885..cd89b5cba8d2 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1358,6 +1358,7 @@ struct event_modifier {
int exclude_GH;
int sample_read;
int pinned;
+ int weak;
};

static int get_event_modifier(struct event_modifier *mod, char *str,
@@ -1376,6 +1377,7 @@ static int get_event_modifier(struct event_modifier *mod, char *str,

int exclude = eu | ek | eh;
int exclude_GH = evsel ? evsel->exclude_GH : 0;
+ int weak = 0;

memset(mod, 0, sizeof(*mod));

@@ -1413,6 +1415,8 @@ static int get_event_modifier(struct event_modifier *mod, char *str,
sample_read = 1;
} else if (*str == 'D') {
pinned = 1;
+ } else if (*str == 'W') {
+ weak = 1;
} else
break;

@@ -1443,6 +1447,7 @@ static int get_event_modifier(struct event_modifier *mod, char *str,
mod->exclude_GH = exclude_GH;
mod->sample_read = sample_read;
mod->pinned = pinned;
+ mod->weak = weak;

return 0;
}
@@ -1456,7 +1461,7 @@ static int check_modifier(char *str)
char *p = str;

/* The sizeof includes 0 byte as well. */
- if (strlen(str) > (sizeof("ukhGHpppPSDI") - 1))
+ if (strlen(str) > (sizeof("ukhGHpppPSDIW") - 1))
return -1;

while (*p) {
@@ -1496,6 +1501,7 @@ int parse_events__modifier_event(struct list_head *list, char *str, bool add)
evsel->exclude_GH = mod.exclude_GH;
evsel->sample_read = mod.sample_read;
evsel->precise_max = mod.precise_max;
+ evsel->weak_group = mod.weak;

if (perf_evsel__is_group_leader(evsel))
evsel->attr.pinned = mod.pinned;
diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
index c42edeac451f..fdb5bb52f01f 100644
--- a/tools/perf/util/parse-events.l
+++ b/tools/perf/util/parse-events.l
@@ -161,7 +161,7 @@ name [a-zA-Z_*?][a-zA-Z0-9_*?.]*
name_minus [a-zA-Z_*?][a-zA-Z0-9\-_*?.:]*
drv_cfg_term [a-zA-Z0-9_\.]+(=[a-zA-Z0-9_*?\.:]+)?
/* If you add a modifier you need to update check_modifier() */
-modifier_event [ukhpPGHSDI]+
+modifier_event [ukhpPGHSDIW]+
modifier_bp [rwx]{1,3}

%%
--
2.9.4