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In-Reply-To: <1435607735-6332-2-git-send-email-kan.liang@intel.com>
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	<1435607735-6332-2-git-send-email-kan.liang@intel.com>
Date: Tue, 30 Jun 2015 08:52:02 -0700
Message-ID: <CABPqkBRwfeeM9bcHPYQCd0QzC3GrdP+xMA7wWWZ740sBpYNB9g@mail.gmail.com>
Subject: Re: [PATCH 2/2] perf,tools: check and re-organize evsel cpu maps
From: Stephane Eranian <eranian@google.com>
To: "Liang, Kan" <kan.liang@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        David Ahern <dsahern@gmail.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        "mingo@redhat.com" <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Jun 29, 2015 at 12:55 PM, <kan.liang@intel.com> wrote:
>
> From: Kan Liang <kan.liang@intel.com>
>
> Some PMU events have cpumask, e.g uncore events. The cpu list set by
> user may be incompatible with event's cpumask.
> This patch will check the user defined cpu list. If the incompatible cpu
> is found, it will warn the user and discard the incompatible cpu. Only
> available cpu can be stored in evsel->cpus->map. If there is no cpu from
> cpu list compatible with event's cpumask. It will error out.
>
> Here is an example.
> According to cpumask, uncore should only available on CPU0 and CPU18.
> So the S0-C1 for uncore should not count.
>
I don't think this is correct. The cpumask is a default set of CPUs to
be used by
perf. The cpumask does not indicate the ONLY CPUs on which to monitor. It
is just a default. You can monitor an uncore event using a CPU not listed in
the cpumask, unless the kernel code has changed recently. If you are not
on the default CPUs, the kernel will IPI.

>
> Without this patch
>  $ sudo ./perf stat -e cycles,uncore_imc_0/cas_count_read/ -C0,1,18
> --per-core sleep 2
>
>  Performance counter stats for 'CPU(s) 0,1,18':
>
> S0-C0           1            6749638      cycles
> S0-C0           1               0.83 MiB  uncore_imc_0/cas_count_read/
> (100.00%)
> S0-C1           1             232421      cycles
> S0-C1           1               0.83 MiB  uncore_imc_0/cas_count_read/
> S1-C0           1             236997      cycles
> S1-C0           1               0.35 MiB  uncore_imc_0/cas_count_read/
>
>        2.001094019 seconds time elapsed
>
> With this patch
>  $ perf stat -e cycles,uncore_imc_0/cas_count_read/ -C0,1,18 --per-core
> sleep 2
> event uncore_imc_0/cas_count_read/ can only be monitored on CPU 0 18.
> Other CPUs will be discard.
>
>  Performance counter stats for 'CPU(s) 0,1,18':
>
> S0-C0           1            5557406      cycles
> S0-C0           1               0.21 MiB  uncore_imc_0/cas_count_read/
> S0-C1           1            1012534      cycles
> S0-C1           0      <not counted> MiB  uncore_imc_0/cas_count_read/
> S1-C0           1             916130      cycles
> S1-C0           1               0.08 MiB  uncore_imc_0/cas_count_read/
>
>        2.001110843 seconds time elapsed
>
> Signed-off-by: Kan Liang <kan.liang@intel.com>
> ---
>  tools/perf/util/evlist.c | 77 ++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 72 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 6cfdee6..f179379 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1101,6 +1101,71 @@ int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
>         return perf_evlist__mmap_ex(evlist, pages, overwrite, 0, false);
>  }
>
> +static int cmp_ids(const void *a, const void *b)
> +{
> +       return *(int *)a - *(int *)b;
> +}
> +
> +static int perf_evlist__check_evsel_cpus(struct perf_evlist *evlist, struct perf_evsel *evsel)
> +{
> +       const struct cpu_map *cpus = evlist->cpus;
> +       const int ncpus = cpu_map__nr(evlist->cpus);
> +       int j = 0, cpu_nr = 0, tmp = 0;
> +       int i;
> +
> +       /* ensure we process id in increasing order */
> +       qsort(evlist->cpus->map, evlist->cpus->nr, sizeof(int), cmp_ids);
> +
> +       /* find the common cpus between evsel and evlist. */
> +       for (i = 0; i < cpu_map__nr(evsel->cpus);)  {
> +
> +               if (j >= ncpus) {
> +                       evsel->cpus->map[i++] = -1;
> +                       continue;
> +               }
> +               for (; j < ncpus; j++) {
> +                       if (cpus->map[j] < evsel->cpus->map[i])
> +                               continue;
> +                       if (cpus->map[j] == evsel->cpus->map[i]) {
> +                               cpu_nr++;
> +                               j++;
> +                               i++;
> +                       } else
> +                               evsel->cpus->map[i++] = -1;
> +                       break;
> +               }
> +       }
> +
> +       if (cpu_nr == 0) {
> +               pr_warning("event %s cannot be monitored on the given cpus."
> +                          "Please check cpumask\n", evsel->name);
> +               return -1;
> +       }
> +
> +       if (ncpus > cpu_nr)
> +               pr_warning("event %s can only be monitored on CPU", evsel->name);
> +
> +       /* order evsel cpus */
> +       for (i = 0; i < cpu_nr; i++) {
> +               if (evsel->cpus->map[i] == -1) {
> +                       while (evsel->cpus->map[tmp] == -1) {
> +                               tmp++;
> +                               BUG_ON(tmp >= cpu_map__nr(evsel->cpus));
> +                       }
> +                       evsel->cpus->map[i] = evsel->cpus->map[tmp];
> +                       evsel->cpus->map[tmp] = -1;
> +               }
> +               if (ncpus > cpu_nr)
> +                       pr_warning(" %d", evsel->cpus->map[i]);
> +               tmp++;
> +       }
> +       evsel->cpus->nr = cpu_nr;
> +       if (ncpus > cpu_nr)
> +               pr_warning(". Other CPUs will be discard.\n");
> +
> +       return 0;
> +}
> +
>  static int perf_evlist__propagate_maps(struct perf_evlist *evlist,
>                                        struct target *target)
>  {
> @@ -1108,13 +1173,15 @@ static int perf_evlist__propagate_maps(struct perf_evlist *evlist,
>
>         evlist__for_each(evlist, evsel) {
>                 /*
> -                * We already have cpus for evsel (via PMU sysfs) so
> -                * keep it, if there's no target cpu list defined.
> +                * We already have cpus for evsel (via PMU sysfs)
> +                * and target cpu list defined, check if they are
> +                * compatible. If not, discard incompatible cpus.
>                  */
> -               if (evsel->cpus && target->cpu_list)
> -                       cpu_map__put(evsel->cpus);
> +               if (evsel->cpus && target->cpu_list &&
> +                   perf_evlist__check_evsel_cpus(evlist, evsel))
> +                       return -EINVAL;
>
> -               if (!evsel->cpus || target->cpu_list)
> +               if (!evsel->cpus)
>                         evsel->cpus = cpu_map__get(evlist->cpus);
>
>                 evsel->threads = thread_map__get(evlist->threads);
> --
> 1.8.3.1
>
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