Re: [PATCH 2/2] perf,tools: check and re-organize evsel cpu maps

From: Stephane Eranian
Date: Tue Jun 30 2015 - 11:52:13 EST

On Mon, Jun 29, 2015 at 12:55 PM, <kan.liang@xxxxxxxxx> wrote:
>
> From: Kan Liang <kan.liang@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> ---
> 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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