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Date: Mon, 28 Mar 2022 17:56:07 -0300
From: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To: Ian Rogers <irogers@...gle.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>
CC: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Suzuki K Poulose <suzuki.poulose@....com>,
Mike Leach <mike.leach@...aro.org>,
Leo Yan <leo.yan@...aro.org>,
John Garry <john.garry@...wei.com>,
Will Deacon <will@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Kajol Jain <kjain@...ux.ibm.com>,
James Clark <james.clark@....com>,
German Gomez <german.gomez@....com>,
Adrian Hunter <adrian.hunter@...el.com>,
Riccardo Mancini <rickyman7@...il.com>,
Andi Kleen <ak@...ux.intel.com>,
Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
Alexander Antonov <alexander.antonov@...ux.intel.com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
netdev@...r.kernel.org, bpf@...r.kernel.org,
Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/5] perf cpumap: More cpu map reuse by merge.
On March 28, 2022 5:50:21 PM GMT-03:00, Ian Rogers <irogers@...gle.com> wrote:
>On Mon, Mar 28, 2022 at 1:26 PM Arnaldo Carvalho de Melo
><acme@...nel.org> wrote:
>>
>> Em Sun, Mar 27, 2022 at 11:24:11PM -0700, Ian Rogers escreveu:
>> > perf_cpu_map__merge will reuse one of its arguments if they are equal or
>> > the other argument is NULL. The arguments could be reused if it is known
>> > one set of values is a subset of the other. For example, a map of 0-1
>> > and a map of just 0 when merged yields the map of 0-1. Currently a new
>> > map is created rather than adding a reference count to the original 0-1
>> > map.
>> >
>> > Signed-off-by: Ian Rogers <irogers@...gle.com>
>> > ---
>> > tools/lib/perf/cpumap.c | 38 ++++++++++++++++++++++++++++----------
>> > 1 file changed, 28 insertions(+), 10 deletions(-)
>> >
>> > diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
>> > index ee66760f1e63..953bc50b0e41 100644
>> > --- a/tools/lib/perf/cpumap.c
>> > +++ b/tools/lib/perf/cpumap.c
>> > @@ -319,6 +319,29 @@ struct perf_cpu perf_cpu_map__max(struct perf_cpu_map *map)
>> > return map->nr > 0 ? map->map[map->nr - 1] : result;
>> > }
>> >
>> > +/** Is 'b' a subset of 'a'. */
>> > +static bool perf_cpu_map__is_subset(const struct perf_cpu_map *a,
>> > + const struct perf_cpu_map *b)
>> > +{
>> > + int i, j;
>> > +
>> > + if (a == b || !b)
>> > + return true;
>> > + if (!a || b->nr > a->nr)
>> > + return false;
>> > + j = 0;
>> > + for (i = 0; i < a->nr; i++) {
>>
>> Since the kernel bumped the minimum gcc version to one that supports
>> declaring loop variables locally and that perf has been using this since
>> forever:
>>
>> ⬢[acme@...lbox perf]$ grep -r '(int [[:alpha:]] = 0;' tools/perf
>> tools/perf/util/block-info.c: for (int i = 0; i < nr_hpps; i++)
>> tools/perf/util/block-info.c: for (int i = 0; i < nr_hpps; i++) {
>> tools/perf/util/block-info.c: for (int i = 0; i < nr_reps; i++)
>> tools/perf/util/stream.c: for (int i = 0; i < nr_evsel; i++)
>> tools/perf/util/stream.c: for (int i = 0; i < nr_evsel; i++) {
>> tools/perf/util/stream.c: for (int i = 0; i < els->nr_evsel; i++) {
>> tools/perf/util/stream.c: for (int i = 0; i < es_pair->nr_streams; i++) {
>> tools/perf/util/stream.c: for (int i = 0; i < es_base->nr_streams; i++) {
>> tools/perf/util/cpumap.c: for (int j = 0; j < c->nr; j++) {
>> tools/perf/util/mem-events.c: for (int j = 0; j < PERF_MEM_EVENTS__MAX; j++) {
>> tools/perf/util/header.c: for (int i = 0; i < ff->ph->env.nr_hybrid_cpc_nodes; i++) {
>> tools/perf/builtin-diff.c: for (int i = 0; i < num; i++)
>> tools/perf/builtin-diff.c: for (int i = 0; i < pair->block_info->num; i++) {
>> tools/perf/builtin-stat.c: for (int i = 0; i < perf_cpu_map__nr(a->core.cpus); i++) {
>> ⬢[acme@...lbox perf]$
>>
>> And this builds on all my test containers, please use:
>>
>> for (int i = 0, j = 0; i < a->nr; i++)
>>
>> In this case to make the source code more compact.
>
>Ack. We still need to declare 'j' and it is a bit weird to declare j
>before i. Fwiw, Making.config has the CORE_CFLAGS set to gnu99, but
>declaring in the loop is clearly valid in c99.
>
>> > + if (a->map[i].cpu > b->map[j].cpu)
>> > + return false;
>> > + if (a->map[i].cpu == b->map[j].cpu) {
>> > + j++;
>> > + if (j == b->nr)
>> > + return true;
>>
>> Ok, as its guaranteed that cpu_maps are ordered.
>>
>> > + }
>> > + }
>> > + return false;
>> > +}
>> > +
>> > /*
>> > * Merge two cpumaps
>> > *
>> > @@ -335,17 +358,12 @@ struct perf_cpu_map *perf_cpu_map__merge(struct perf_cpu_map *orig,
>> > int i, j, k;
>> > struct perf_cpu_map *merged;
>> >
>> > - if (!orig && !other)
>> > - return NULL;
>> > - if (!orig) {
>> > - perf_cpu_map__get(other);
>> > - return other;
>> > - }
>> > - if (!other)
>> > - return orig;
>> > - if (orig->nr == other->nr &&
>> > - !memcmp(orig->map, other->map, orig->nr * sizeof(struct perf_cpu)))
>> > + if (perf_cpu_map__is_subset(orig, other))
>> > return orig;
>>
>> Can't we have first the introduction of perf_cpu_map__is_subset() and
>> then another patch that gets the refcount, i.e. the four lines below?
>
>I believe that will fail as it'd be an unused static function warning
>and werror.
I thought that it seemed useful enough not to be a static, even if we don't at first export it, i.e. keep it as internal to libperf
>
>Thanks,
>Ian
>
>> > + if (perf_cpu_map__is_subset(other, orig)) {
>> > + perf_cpu_map__put(orig);
>> > + return perf_cpu_map__get(other);
>> > + }
>> >
>> > tmp_len = orig->nr + other->nr;
>> > tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
>> > --
>> > 2.35.1.1021.g381101b075-goog
>>
>> --
>>
>> - Arnaldo
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