From: Rob Herring <robh@kernel.org>
To: Jiri Olsa <jolsa@redhat.com>
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: Fri, 16 Oct 2020 16:39:15 -0500 [thread overview]
Message-ID: <CAL_Jsq+5_uzAdn+rq-rWVACeaMMd4q+ntxxOd5JisOiBzwvDbw@mail.gmail.com> (raw)
In-Reply-To: <20201014110527.GA1349644@krava>
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)?
Rob
WARNING: multiple messages have this Message-ID (diff)
From: Rob Herring <robh@kernel.org>
To: Jiri Olsa <jolsa@redhat.com>
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: Fri, 16 Oct 2020 16:39:15 -0500 [thread overview]
Message-ID: <CAL_Jsq+5_uzAdn+rq-rWVACeaMMd4q+ntxxOd5JisOiBzwvDbw@mail.gmail.com> (raw)
In-Reply-To: <20201014110527.GA1349644@krava>
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)?
Rob
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next prev parent reply other threads:[~2020-10-16 21:39 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 [this message]
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
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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