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From:   Ian Rogers <irogers@google.com>
Date:   Wed, 31 Aug 2022 08:58:49 -0700
Message-ID: <CAP-5=fUxRMSJUemUEcrDuRXpUFj3qNiRFQz1S7=cQrvmfyGYew@mail.gmail.com>
Subject: Re: [PATCH v1 5/8] perf topology: Add core_wide
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Thomas Richter <tmricht@linux.ibm.com>,
        James Clark <james.clark@arm.com>,
        Miaoqian Lin <linmq006@gmail.com>,
        John Garry <john.garry@huawei.com>,
        Zhengjun Xing <zhengjun.xing@linux.intel.com>,
        Florian Fischer <florian.fischer@muhq.space>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        perry.taylor@intel.com, caleb.biggers@intel.com,
        kshipra.bopardikar@intel.com, Stephane Eranian <eranian@google.com>
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On Wed, Aug 31, 2022 at 7:40 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Tue, Aug 30, 2022 at 09:48:43AM -0700, Ian Rogers escreveu:
> > It is possible to optimize metrics when all SMT threads (CPUs) on a
> > core are measuring events in system wide mode. For example, TMA
> > metrics defines CORE_CLKS for Sandybrdige as:
> >
> > if SMT is disabled:
> >   CPU_CLK_UNHALTED.THREAD
> > if SMT is enabled and recording on all SMT threads:
> >   CPU_CLK_UNHALTED.THREAD_ANY / 2
> > if SMT is enabled and not recording on all SMT threads:
> >   (CPU_CLK_UNHALTED.THREAD/2)*
> >   (1+CPU_CLK_UNHALTED.ONE_THREAD_ACTIVE/CPU_CLK_UNHALTED.REF_XCLK )
> >
> > That is two more events are necessary when not gathering counts on all
> > SMT threads. To distinguish all SMT threads on a core vs system wide
> > (all CPUs) call the new property core wide.  Add a core wide test that
> > determines the property from user requested CPUs, the topology and
> > system wide. System wide is required as other processes running on a
> > SMT thread will change the counts.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/util/cputopo.c | 46 +++++++++++++++++++++++++++++++++++++++
> >  tools/perf/util/cputopo.h |  3 +++
> >  tools/perf/util/smt.c     | 14 ++++++++++++
> >  tools/perf/util/smt.h     |  7 ++++++
> >  4 files changed, 70 insertions(+)
> >
> > diff --git a/tools/perf/util/cputopo.c b/tools/perf/util/cputopo.c
> > index 511002e52714..1a3ff6449158 100644
> > --- a/tools/perf/util/cputopo.c
> > +++ b/tools/perf/util/cputopo.c
> > @@ -172,6 +172,52 @@ bool cpu_topology__smt_on(const struct cpu_topology *topology)
> >       return false;
> >  }
> >
> > +bool cpu_topology__core_wide(const struct cpu_topology *topology,
> > +                          const char *user_requested_cpu_list)
> > +{
> > +     struct perf_cpu_map *user_requested_cpus;
> > +
> > +     /*
> > +      * If user_requested_cpu_list is empty then all CPUs are recorded and so
> > +      * core_wide is true.
> > +      */
> > +     if (!user_requested_cpu_list)
> > +             return true;
> > +
> > +     user_requested_cpus = perf_cpu_map__new(user_requested_cpu_list);
>
> Don't we need a NULL test here?

No, NULL is a valid perf_cpu_map, one with no values in it. For
example, see here:
https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/lib/perf/cpumap.c?h=perf/core#n266
So there's no way to tell an error (ENOMEM) from an empty map. My
suggestion is a rewrite of perf_cpu_map, I'd like to do this in a new
"libperf2" which has a more permissive than GPL license like libbpf.
That is out-of-scope here.

Thanks,
Ian

> > +     /* Check that every user requested CPU is the complete set of SMT threads on a core. */
> > +     for (u32 i = 0; i < topology->core_cpus_lists; i++) {
> > +             const char *core_cpu_list = topology->core_cpus_list[i];
> > +             struct perf_cpu_map *core_cpus = perf_cpu_map__new(core_cpu_list);
>
> Here too, no?
>
> > +             struct perf_cpu cpu;
> > +             int idx;
> > +             bool has_first, first = true;
> > +
> > +             perf_cpu_map__for_each_cpu(cpu, idx, core_cpus) {
> > +                     if (first) {
> > +                             has_first = perf_cpu_map__has(user_requested_cpus, cpu);
> > +                             first = false;
> > +                     } else {
> > +                             /*
> > +                              * If the first core CPU is user requested then
> > +                              * all subsequent CPUs in the core must be user
> > +                              * requested too. If the first CPU isn't user
> > +                              * requested then none of the others must be
> > +                              * too.
> > +                              */
> > +                             if (perf_cpu_map__has(user_requested_cpus, cpu) != has_first) {
> > +                                     perf_cpu_map__put(core_cpus);
> > +                                     perf_cpu_map__put(user_requested_cpus);
> > +                                     return false;
> > +                             }
> > +                     }
> > +             }
> > +             perf_cpu_map__put(core_cpus);
> > +     }
> > +     perf_cpu_map__put(user_requested_cpus);
> > +     return true;
> > +}
> > +
> >  static bool has_die_topology(void)
> >  {
> >       char filename[MAXPATHLEN];
> > diff --git a/tools/perf/util/cputopo.h b/tools/perf/util/cputopo.h
> > index 469db775a13c..969e5920a00e 100644
> > --- a/tools/perf/util/cputopo.h
> > +++ b/tools/perf/util/cputopo.h
> > @@ -60,6 +60,9 @@ struct cpu_topology *cpu_topology__new(void);
> >  void cpu_topology__delete(struct cpu_topology *tp);
> >  /* Determine from the core list whether SMT was enabled. */
> >  bool cpu_topology__smt_on(const struct cpu_topology *topology);
> > +/* Are the sets of SMT siblings all enabled or all disabled in user_requested_cpus. */
> > +bool cpu_topology__core_wide(const struct cpu_topology *topology,
> > +                          const char *user_requested_cpu_list);
> >
> >  struct numa_topology *numa_topology__new(void);
> >  void numa_topology__delete(struct numa_topology *tp);
> > diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
> > index ce90c4ee4138..994e9e418227 100644
> > --- a/tools/perf/util/smt.c
> > +++ b/tools/perf/util/smt.c
> > @@ -21,3 +21,17 @@ bool smt_on(const struct cpu_topology *topology)
> >       cached = true;
> >       return cached_result;
> >  }
> > +
> > +bool core_wide(bool system_wide, const char *user_requested_cpu_list,
> > +            const struct cpu_topology *topology)
> > +{
> > +     /* If not everything running on a core is being recorded then we can't use core_wide. */
> > +     if (!system_wide)
> > +             return false;
> > +
> > +     /* Cheap case that SMT is disabled and therefore we're inherently core_wide. */
> > +     if (!smt_on(topology))
> > +             return true;
> > +
> > +     return cpu_topology__core_wide(topology, user_requested_cpu_list);
> > +}
> > diff --git a/tools/perf/util/smt.h b/tools/perf/util/smt.h
> > index e26999c6b8d4..ae9095f2c38c 100644
> > --- a/tools/perf/util/smt.h
> > +++ b/tools/perf/util/smt.h
> > @@ -7,4 +7,11 @@ struct cpu_topology;
> >  /* Returns true if SMT (aka hyperthreading) is enabled. */
> >  bool smt_on(const struct cpu_topology *topology);
> >
> > +/*
> > + * Returns true when system wide and all SMT threads for a core are in the
> > + * user_requested_cpus map.
> > + */
> > +bool core_wide(bool system_wide, const char *user_requested_cpu_list,
> > +            const struct cpu_topology *topology);
> > +
> >  #endif /* __SMT_H */
> > --
> > 2.37.2.672.g94769d06f0-goog
>
> --
>
> - Arnaldo