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From: Jiri Olsa <jolsa@redhat.com>
To: Rob Herring <robh@kernel.org>
Cc: Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Raphael Gault <raphael.gault@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Ian Rogers <irogers@google.com>,
	Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>,
	Itaru Kitayama <itaru.kitayama@gmail.com>
Subject: Re: [PATCH v4 4/9] libperf: Add libperf_evsel__mmap()
Date: Tue, 20 Oct 2020 17:35:27 +0200	[thread overview]
Message-ID: <20201020153527.GD2113901@krava> (raw)
In-Reply-To: <CAL_JsqKpbdvxn7w1PSWrE7fLP+NtwwxtTjr02yxSkjy00yN9Xw@mail.gmail.com>

On Tue, Oct 20, 2020 at 09:38:13AM -0500, Rob Herring wrote:
> On Mon, Oct 19, 2020 at 3:15 PM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > On Fri, Oct 16, 2020 at 04:39:15PM -0500, Rob Herring wrote:
> > > On Wed, Oct 14, 2020 at 6:05 AM Jiri Olsa <jolsa@redhat.com> wrote:
> > > >
> > > > On Thu, Oct 01, 2020 at 09:01:11AM -0500, Rob Herring wrote:
> > > >
> > > > SNIP
> > > >
> > > > >
> > > > > +void *perf_evsel__mmap(struct perf_evsel *evsel, int pages)
> > > > > +{
> > > > > +     int ret;
> > > > > +     struct perf_mmap *map;
> > > > > +     struct perf_mmap_param mp = {
> > > > > +             .prot = PROT_READ | PROT_WRITE,
> > > > > +     };
> > > > > +
> > > > > +     if (FD(evsel, 0, 0) < 0)
> > > > > +             return NULL;
> > > > > +
> > > > > +     mp.mask = (pages * page_size) - 1;
> > > > > +
> > > > > +     map = zalloc(sizeof(*map));
> > > > > +     if (!map)
> > > > > +             return NULL;
> > > > > +
> > > > > +     perf_mmap__init(map, NULL, false, NULL);
> > > > > +
> > > > > +     ret = perf_mmap__mmap(map, &mp, FD(evsel, 0, 0), 0);
> > > >
> > > > hum, so you map event for FD(0,0) but later in perf_evsel__read
> > > > you allow to read any cpu/thread combination ending up reading
> > > > data from FD(0,0) map:
> > > >
> > > >         int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
> > > >                              struct perf_counts_values *count)
> > > >         {
> > > >                 size_t size = perf_evsel__read_size(evsel);
> > > >
> > > >                 memset(count, 0, sizeof(*count));
> > > >
> > > >                 if (FD(evsel, cpu, thread) < 0)
> > > >                         return -EINVAL;
> > > >
> > > >                 if (evsel->mmap && !perf_mmap__read_self(evsel->mmap, count))
> > > >                         return 0;
> > > >
> > > >
> > > > I think we should either check cpu == 0, thread == 0, or make it
> > > > general and store perf_evsel::mmap in xyarray as we do for fds
> > >
> > > The mmapped read will actually fail and then we fallback here. My main
> > > concern though is adding more overhead on a feature that's meant to be
> > > low overhead (granted, it's not much). Maybe we could add checks on
> > > the mmap that we've opened the event with pid == 0 and cpu == -1 (so
> > > only 1 FD)?
> >
> > but then you limit this just for single fd.. having mmap as xyarray
> > would not be that bad and perf_evsel__mmap will call perf_mmap__mmap
> > for each defined cpu/thread .. so it depends on user how fast this
> > will be - how many maps needs to be created/mmaped
> 
> Given userspace access fails for anything other than the calling
> thread and all cpus, how would more than 1 mmap be useful here?

I'm not sure what you mean by fail in here.. you need mmap for each
event fd you want to read from

in the example below we read stats from all cpus via perf_evsel__read,
if we insert this call after perf_evsel__open:

  perf_evsel__mmap(cpus, NULL);

that maps page for each event, then perf_evsel__read
could go through the fast code, no?

> 
> If we did want multiple mmaps, wouldn't we just use the evlist API in
> that case? It already does all that.

we could, but I see this as a separate perf_evsel interface, and if
we allow to have perf_evsel__mmap I think it should follow the
cpus/threads it's open for

jirka


---
static int test_stat_cpu(void)
{
        struct perf_cpu_map *cpus;
        struct perf_evsel *evsel;
        struct perf_event_attr attr = {
                .type   = PERF_TYPE_SOFTWARE,
                .config = PERF_COUNT_SW_CPU_CLOCK,
        };
        int err, cpu, tmp;

        cpus = perf_cpu_map__new(NULL);
        __T("failed to create cpus", cpus);

        evsel = perf_evsel__new(&attr);
        __T("failed to create evsel", evsel);

        err = perf_evsel__open(evsel, cpus, NULL);
        __T("failed to open evsel", err == 0);

        perf_cpu_map__for_each_cpu(cpu, tmp, cpus) {
                struct perf_counts_values counts = { .val = 0 };

                perf_evsel__read(evsel, cpu, 0, &counts);
                __T("failed to read value for evsel", counts.val != 0);
        }

        perf_evsel__close(evsel);
        perf_evsel__delete(evsel);

        perf_cpu_map__put(cpus);
        return 0;
}


WARNING: multiple messages have this Message-ID
From: Jiri Olsa <jolsa@redhat.com>
To: Rob Herring <robh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Ian Rogers <irogers@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Raphael Gault <raphael.gault@arm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Itaru Kitayama <itaru.kitayama@gmail.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v4 4/9] libperf: Add libperf_evsel__mmap()
Date: Tue, 20 Oct 2020 17:35:27 +0200	[thread overview]
Message-ID: <20201020153527.GD2113901@krava> (raw)
In-Reply-To: <CAL_JsqKpbdvxn7w1PSWrE7fLP+NtwwxtTjr02yxSkjy00yN9Xw@mail.gmail.com>

On Tue, Oct 20, 2020 at 09:38:13AM -0500, Rob Herring wrote:
> On Mon, Oct 19, 2020 at 3:15 PM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > On Fri, Oct 16, 2020 at 04:39:15PM -0500, Rob Herring wrote:
> > > On Wed, Oct 14, 2020 at 6:05 AM Jiri Olsa <jolsa@redhat.com> wrote:
> > > >
> > > > On Thu, Oct 01, 2020 at 09:01:11AM -0500, Rob Herring wrote:
> > > >
> > > > SNIP
> > > >
> > > > >
> > > > > +void *perf_evsel__mmap(struct perf_evsel *evsel, int pages)
> > > > > +{
> > > > > +     int ret;
> > > > > +     struct perf_mmap *map;
> > > > > +     struct perf_mmap_param mp = {
> > > > > +             .prot = PROT_READ | PROT_WRITE,
> > > > > +     };
> > > > > +
> > > > > +     if (FD(evsel, 0, 0) < 0)
> > > > > +             return NULL;
> > > > > +
> > > > > +     mp.mask = (pages * page_size) - 1;
> > > > > +
> > > > > +     map = zalloc(sizeof(*map));
> > > > > +     if (!map)
> > > > > +             return NULL;
> > > > > +
> > > > > +     perf_mmap__init(map, NULL, false, NULL);
> > > > > +
> > > > > +     ret = perf_mmap__mmap(map, &mp, FD(evsel, 0, 0), 0);
> > > >
> > > > hum, so you map event for FD(0,0) but later in perf_evsel__read
> > > > you allow to read any cpu/thread combination ending up reading
> > > > data from FD(0,0) map:
> > > >
> > > >         int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
> > > >                              struct perf_counts_values *count)
> > > >         {
> > > >                 size_t size = perf_evsel__read_size(evsel);
> > > >
> > > >                 memset(count, 0, sizeof(*count));
> > > >
> > > >                 if (FD(evsel, cpu, thread) < 0)
> > > >                         return -EINVAL;
> > > >
> > > >                 if (evsel->mmap && !perf_mmap__read_self(evsel->mmap, count))
> > > >                         return 0;
> > > >
> > > >
> > > > I think we should either check cpu == 0, thread == 0, or make it
> > > > general and store perf_evsel::mmap in xyarray as we do for fds
> > >
> > > The mmapped read will actually fail and then we fallback here. My main
> > > concern though is adding more overhead on a feature that's meant to be
> > > low overhead (granted, it's not much). Maybe we could add checks on
> > > the mmap that we've opened the event with pid == 0 and cpu == -1 (so
> > > only 1 FD)?
> >
> > but then you limit this just for single fd.. having mmap as xyarray
> > would not be that bad and perf_evsel__mmap will call perf_mmap__mmap
> > for each defined cpu/thread .. so it depends on user how fast this
> > will be - how many maps needs to be created/mmaped
> 
> Given userspace access fails for anything other than the calling
> thread and all cpus, how would more than 1 mmap be useful here?

I'm not sure what you mean by fail in here.. you need mmap for each
event fd you want to read from

in the example below we read stats from all cpus via perf_evsel__read,
if we insert this call after perf_evsel__open:

  perf_evsel__mmap(cpus, NULL);

that maps page for each event, then perf_evsel__read
could go through the fast code, no?

> 
> If we did want multiple mmaps, wouldn't we just use the evlist API in
> that case? It already does all that.

we could, but I see this as a separate perf_evsel interface, and if
we allow to have perf_evsel__mmap I think it should follow the
cpus/threads it's open for

jirka


---
static int test_stat_cpu(void)
{
        struct perf_cpu_map *cpus;
        struct perf_evsel *evsel;
        struct perf_event_attr attr = {
                .type   = PERF_TYPE_SOFTWARE,
                .config = PERF_COUNT_SW_CPU_CLOCK,
        };
        int err, cpu, tmp;

        cpus = perf_cpu_map__new(NULL);
        __T("failed to create cpus", cpus);

        evsel = perf_evsel__new(&attr);
        __T("failed to create evsel", evsel);

        err = perf_evsel__open(evsel, cpus, NULL);
        __T("failed to open evsel", err == 0);

        perf_cpu_map__for_each_cpu(cpu, tmp, cpus) {
                struct perf_counts_values counts = { .val = 0 };

                perf_evsel__read(evsel, cpu, 0, &counts);
                __T("failed to read value for evsel", counts.val != 0);
        }

        perf_evsel__close(evsel);
        perf_evsel__delete(evsel);

        perf_cpu_map__put(cpus);
        return 0;
}


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-10-20 15:35 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01 14:01 [PATCH v4 0/9] libperf and arm64 userspace counter access support Rob Herring
2020-10-01 14:01 ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 1/9] arm64: pmu: Add function implementation to update event index in userpage Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 2/9] arm64: perf: Enable pmu counter direct access for perf event on armv8 Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-11-13 18:06   ` Mark Rutland
2020-11-13 18:06     ` Mark Rutland
2020-11-19 18:35     ` Rob Herring
2020-11-19 18:35       ` Rob Herring
2020-11-19 19:15     ` Will Deacon
2020-11-19 19:15       ` Will Deacon
2020-11-20 20:03       ` Rob Herring
2020-11-20 20:03         ` Rob Herring
2020-11-20 22:08         ` Rob Herring
2020-11-20 22:08           ` Rob Herring
2020-12-02 14:57         ` Rob Herring
2020-12-02 14:57           ` Rob Herring
2021-01-07  0:17           ` Rob Herring
2021-01-07  0:17             ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 3/9] tools/include: Add an initial math64.h Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 4/9] libperf: Add libperf_evsel__mmap() Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-14 11:05   ` Jiri Olsa
2020-10-14 11:05     ` Jiri Olsa
2020-10-16 21:39     ` Rob Herring
2020-10-16 21:39       ` Rob Herring
2020-10-19 20:15       ` Jiri Olsa
2020-10-19 20:15         ` Jiri Olsa
2020-10-20 14:38         ` Rob Herring
2020-10-20 14:38           ` Rob Herring
2020-10-20 15:35           ` Jiri Olsa [this message]
2020-10-20 15:35             ` Jiri Olsa
2020-10-20 17:11             ` Rob Herring
2020-10-20 17:11               ` Rob Herring
2020-10-21 11:24               ` Jiri Olsa
2020-10-21 11:24                 ` Jiri Olsa
2020-11-05 16:19                 ` Rob Herring
2020-11-05 16:19                   ` Rob Herring
2020-11-05 22:41                   ` Jiri Olsa
2020-11-05 22:41                     ` Jiri Olsa
2020-11-06 21:56                     ` Rob Herring
2020-11-06 21:56                       ` Rob Herring
2020-11-11 12:00                       ` Jiri Olsa
2020-11-11 12:00                         ` Jiri Olsa
2020-11-11 14:50                         ` Rob Herring
2020-11-11 14:50                           ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 5/9] libperf: tests: Add support for verbose printing Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 6/9] libperf: Add support for user space counter access Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 7/9] libperf: Add arm64 support to perf_mmap__read_self() Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 8/9] perf: arm64: Add test for userspace counter access on heterogeneous systems Rob Herring
2020-10-01 14:01   ` Rob Herring
2020-10-01 14:01 ` [PATCH v4 9/9] Documentation: arm64: Document PMU counters access from userspace Rob Herring
2020-10-01 14:01   ` Rob Herring

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