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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: Mon, 19 Oct 2020 22:15:41 +0200	[thread overview]
Message-ID: <20201019201541.GN1461394@krava> (raw)
In-Reply-To: <CAL_Jsq+5_uzAdn+rq-rWVACeaMMd4q+ntxxOd5JisOiBzwvDbw@mail.gmail.com>

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

jirka


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: Mon, 19 Oct 2020 22:15:41 +0200	[thread overview]
Message-ID: <20201019201541.GN1461394@krava> (raw)
In-Reply-To: <CAL_Jsq+5_uzAdn+rq-rWVACeaMMd4q+ntxxOd5JisOiBzwvDbw@mail.gmail.com>

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

jirka


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  reply	other threads:[~2020-10-19 20:15 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 [this message]
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
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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