2022-03-17 23:50:32

by Ian Rogers

Subject: [PATCH v2] perf evlist: Avoid iteration for empty evlist.

As seen with 'perf stat --null ..' and reported in:
https://lore.kernel.org/lkml/[email protected]/

v2. Avoids setting evsel in the empty list case as suggested by Jiri
Olsa <[email protected]>.
Fixes: 472832d2c000 ("perf evlist: Refactor evlist__for_each_cpu()")
Signed-off-by: Ian Rogers <[email protected]>
---
tools/perf/util/evlist.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 8134d45e2164..9bb79e049957 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -346,7 +346,7 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
{
struct evlist_cpu_iterator itr = {
.container = evlist,
- .evsel = evlist__first(evlist),
+ .evsel = NULL,
.cpu_map_idx = 0,
.evlist_cpu_map_idx = 0,
.evlist_cpu_map_nr = perf_cpu_map__nr(evlist->core.all_cpus),
@@ -354,16 +354,22 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
.affinity = affinity,
};

- if (itr.affinity) {
- itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
- affinity__set(itr.affinity, itr.cpu.cpu);
- itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
- /*
- * If this CPU isn't in the evsel's cpu map then advance through
- * the list.
- */
- if (itr.cpu_map_idx == -1)
- evlist_cpu_iterator__next(&itr);
+ if (evlist__empty(evlist)) {
+ /* Ensure the empty list doesn't iterate. */
+ itr.evlist_cpu_map_idx = itr.evlist_cpu_map_nr;
+ } else {
+ itr.evsel = evlist__first(evlist);
+ if (itr.affinity) {
+ itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
+ affinity__set(itr.affinity, itr.cpu.cpu);
+ itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
+ /*
+ * If this CPU isn't in the evsel's cpu map then advance
+ * through the list.
+ */
+ if (itr.cpu_map_idx == -1)
+ evlist_cpu_iterator__next(&itr);
+ }
}
return itr;
}
--
2.35.1.894.gb6a874cedc-goog

2022-03-18 16:48:23

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH v2] perf evlist: Avoid iteration for empty evlist.

Em Thu, Mar 17, 2022 at 04:16:43PM -0700, Ian Rogers escreveu:
> As seen with 'perf stat --null ..' and reported in:
> https://lore.kernel.org/lkml/[email protected]/
>
> v2. Avoids setting evsel in the empty list case as suggested by Jiri
> Olsa <[email protected]>.
> Fixes: 472832d2c000 ("perf evlist: Refactor evlist__for_each_cpu()")
> Signed-off-by: Ian Rogers <[email protected]>

Thanks, replaced v1 with this new one.

- Arnaldo

> ---
> tools/perf/util/evlist.c | 28 +++++++++++++++++-----------
> 1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 8134d45e2164..9bb79e049957 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -346,7 +346,7 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
> {
> struct evlist_cpu_iterator itr = {
> .container = evlist,
> - .evsel = evlist__first(evlist),
> + .evsel = NULL,
> .cpu_map_idx = 0,
> .evlist_cpu_map_idx = 0,
> .evlist_cpu_map_nr = perf_cpu_map__nr(evlist->core.all_cpus),
> @@ -354,16 +354,22 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
> .affinity = affinity,
> };
>
> - if (itr.affinity) {
> - itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
> - affinity__set(itr.affinity, itr.cpu.cpu);
> - itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
> - /*
> - * If this CPU isn't in the evsel's cpu map then advance through
> - * the list.
> - */
> - if (itr.cpu_map_idx == -1)
> - evlist_cpu_iterator__next(&itr);
> + if (evlist__empty(evlist)) {
> + /* Ensure the empty list doesn't iterate. */
> + itr.evlist_cpu_map_idx = itr.evlist_cpu_map_nr;
> + } else {
> + itr.evsel = evlist__first(evlist);
> + if (itr.affinity) {
> + itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
> + affinity__set(itr.affinity, itr.cpu.cpu);
> + itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
> + /*
> + * If this CPU isn't in the evsel's cpu map then advance
> + * through the list.
> + */
> + if (itr.cpu_map_idx == -1)
> + evlist_cpu_iterator__next(&itr);
> + }
> }
> return itr;
> }
> --
> 2.35.1.894.gb6a874cedc-goog

--

- Arnaldo

2022-03-21 05:22:11

by Jiri Olsa

Subject: Re: [PATCH v2] perf evlist: Avoid iteration for empty evlist.

On Thu, Mar 17, 2022 at 04:16:43PM -0700, Ian Rogers wrote:
> As seen with 'perf stat --null ..' and reported in:
> https://lore.kernel.org/lkml/[email protected]/
>
> v2. Avoids setting evsel in the empty list case as suggested by Jiri
> Olsa <[email protected]>.
> Fixes: 472832d2c000 ("perf evlist: Refactor evlist__for_each_cpu()")
> Signed-off-by: Ian Rogers <[email protected]>

Acked-by: Jiri Olsa <[email protected]>

thanks,
jirka

> ---
> tools/perf/util/evlist.c | 28 +++++++++++++++++-----------
> 1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 8134d45e2164..9bb79e049957 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -346,7 +346,7 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
> {
> struct evlist_cpu_iterator itr = {
> .container = evlist,
> - .evsel = evlist__first(evlist),
> + .evsel = NULL,
> .cpu_map_idx = 0,
> .evlist_cpu_map_idx = 0,
> .evlist_cpu_map_nr = perf_cpu_map__nr(evlist->core.all_cpus),
> @@ -354,16 +354,22 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
> .affinity = affinity,
> };
>
> - if (itr.affinity) {
> - itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
> - affinity__set(itr.affinity, itr.cpu.cpu);
> - itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
> - /*
> - * If this CPU isn't in the evsel's cpu map then advance through
> - * the list.
> - */
> - if (itr.cpu_map_idx == -1)
> - evlist_cpu_iterator__next(&itr);
> + if (evlist__empty(evlist)) {
> + /* Ensure the empty list doesn't iterate. */
> + itr.evlist_cpu_map_idx = itr.evlist_cpu_map_nr;
> + } else {
> + itr.evsel = evlist__first(evlist);
> + if (itr.affinity) {
> + itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
> + affinity__set(itr.affinity, itr.cpu.cpu);
> + itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
> + /*
> + * If this CPU isn't in the evsel's cpu map then advance
> + * through the list.
> + */
> + if (itr.cpu_map_idx == -1)
> + evlist_cpu_iterator__next(&itr);
> + }
> }
> return itr;
> }
> --
> 2.35.1.894.gb6a874cedc-goog
>