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From: Rob Herring <robh@kernel.org>
To: 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>,
	Jiri Olsa <jolsa@redhat.com>, Mark Rutland <mark.rutland@arm.com>
Cc: Ian Rogers <irogers@google.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	honnappa.nagarahalli@arm.com, Zachary.Leaf@arm.com,
	Raphael Gault <raphael.gault@arm.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Itaru Kitayama <itaru.kitayama@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v6 10/10] Documentation: arm64: Document PMU counters access from userspace
Date: Wed, 10 Mar 2021 17:08:37 -0700	[thread overview]
Message-ID: <20210311000837.3630499-11-robh@kernel.org> (raw)
In-Reply-To: <20210311000837.3630499-1-robh@kernel.org>

From: Raphael Gault <raphael.gault@arm.com>

Add a documentation file to describe the access to the pmu hardware
counters from userspace

Signed-off-by: Raphael Gault <raphael.gault@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
---
v6:
  - Update the chained event section with attr.config1 details
v2:
  - Update links to test examples

Changes from Raphael's v4:
  - Convert to rSt
  - Update chained event status
  - Add section for heterogeneous systems
---
 Documentation/arm64/index.rst                 |  1 +
 .../arm64/perf_counter_user_access.rst        | 60 +++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 Documentation/arm64/perf_counter_user_access.rst

diff --git a/Documentation/arm64/index.rst b/Documentation/arm64/index.rst
index 97d65ba12a35..eb7b1cabbf08 100644
--- a/Documentation/arm64/index.rst
+++ b/Documentation/arm64/index.rst
@@ -18,6 +18,7 @@ ARM64 Architecture
     memory
     memory-tagging-extension
     perf
+    perf_counter_user_access
     pointer-authentication
     silicon-errata
     sve
diff --git a/Documentation/arm64/perf_counter_user_access.rst b/Documentation/arm64/perf_counter_user_access.rst
new file mode 100644
index 000000000000..a42800e72458
--- /dev/null
+++ b/Documentation/arm64/perf_counter_user_access.rst
@@ -0,0 +1,60 @@
+=============================================
+Access to PMU hardware counter from userspace
+=============================================
+
+Overview
+--------
+The perf userspace tool relies on the PMU to monitor events. It offers an
+abstraction layer over the hardware counters since the underlying
+implementation is cpu-dependent.
+Arm64 allows userspace tools to have access to the registers storing the
+hardware counters' values directly.
+
+This targets specifically self-monitoring tasks in order to reduce the overhead
+by directly accessing the registers without having to go through the kernel.
+
+How-to
+------
+The focus is set on the armv8 pmuv3 which makes sure that the access to the pmu
+registers is enabled and that the userspace has access to the relevant
+information in order to use them.
+
+In order to have access to the hardware counter it is necessary to open the event
+using the perf tool interface: the sys_perf_event_open syscall returns a fd which
+can subsequently be used with the mmap syscall in order to retrieve a page of
+memory containing information about the event.
+The PMU driver uses this page to expose to the user the hardware counter's
+index and other necessary data. Using this index enables the user to access the
+PMU registers using the `mrs` instruction.
+
+The userspace access is supported in libperf using the perf_evsel__mmap()
+and perf_evsel__read() functions. See `tools/lib/perf/tests/test-evsel.c`_ for
+an example.
+
+About heterogeneous systems
+---------------------------
+On heterogeneous systems such as big.LITTLE, userspace PMU counter access can
+only be enabled when the tasks are pinned to a homogeneous subset of cores and
+the corresponding PMU instance is opened by specifying the 'type' attribute.
+The use of generic event types is not supported in this case.
+
+Have a look at `tools/perf/arch/arm64/tests/user-events.c`_ for an example. It
+can be run using the perf tool to check that the access to the registers works
+correctly from userspace:
+
+.. code-block:: sh
+
+  perf test -v user
+
+About chained events and 64-bit counters
+----------------------------------------
+Chained events are not supported in conjunction with userspace counter
+access. If a 64-bit counter is requested (attr.config1:0), then
+userspace access must also be requested with attr.config1:1 set. This
+will disable counter chaining. The 'pmc_width' in the user page will
+indicate the actual width of the counter which could be only 32-bits
+depending on event and PMU features.
+
+.. Links
+.. _tools/perf/arch/arm64/tests/user-events.c:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c
-- 
2.27.0


WARNING: multiple messages have this Message-ID
From: Rob Herring <robh@kernel.org>
To: 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>,
	Jiri Olsa <jolsa@redhat.com>, Mark Rutland <mark.rutland@arm.com>
Cc: Ian Rogers <irogers@google.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	honnappa.nagarahalli@arm.com, Zachary.Leaf@arm.com,
	Raphael Gault <raphael.gault@arm.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Itaru Kitayama <itaru.kitayama@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v6 10/10] Documentation: arm64: Document PMU counters access from userspace
Date: Wed, 10 Mar 2021 17:08:37 -0700	[thread overview]
Message-ID: <20210311000837.3630499-11-robh@kernel.org> (raw)
In-Reply-To: <20210311000837.3630499-1-robh@kernel.org>

From: Raphael Gault <raphael.gault@arm.com>

Add a documentation file to describe the access to the pmu hardware
counters from userspace

Signed-off-by: Raphael Gault <raphael.gault@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
---
v6:
  - Update the chained event section with attr.config1 details
v2:
  - Update links to test examples

Changes from Raphael's v4:
  - Convert to rSt
  - Update chained event status
  - Add section for heterogeneous systems
---
 Documentation/arm64/index.rst                 |  1 +
 .../arm64/perf_counter_user_access.rst        | 60 +++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 Documentation/arm64/perf_counter_user_access.rst

diff --git a/Documentation/arm64/index.rst b/Documentation/arm64/index.rst
index 97d65ba12a35..eb7b1cabbf08 100644
--- a/Documentation/arm64/index.rst
+++ b/Documentation/arm64/index.rst
@@ -18,6 +18,7 @@ ARM64 Architecture
     memory
     memory-tagging-extension
     perf
+    perf_counter_user_access
     pointer-authentication
     silicon-errata
     sve
diff --git a/Documentation/arm64/perf_counter_user_access.rst b/Documentation/arm64/perf_counter_user_access.rst
new file mode 100644
index 000000000000..a42800e72458
--- /dev/null
+++ b/Documentation/arm64/perf_counter_user_access.rst
@@ -0,0 +1,60 @@
+=============================================
+Access to PMU hardware counter from userspace
+=============================================
+
+Overview
+--------
+The perf userspace tool relies on the PMU to monitor events. It offers an
+abstraction layer over the hardware counters since the underlying
+implementation is cpu-dependent.
+Arm64 allows userspace tools to have access to the registers storing the
+hardware counters' values directly.
+
+This targets specifically self-monitoring tasks in order to reduce the overhead
+by directly accessing the registers without having to go through the kernel.
+
+How-to
+------
+The focus is set on the armv8 pmuv3 which makes sure that the access to the pmu
+registers is enabled and that the userspace has access to the relevant
+information in order to use them.
+
+In order to have access to the hardware counter it is necessary to open the event
+using the perf tool interface: the sys_perf_event_open syscall returns a fd which
+can subsequently be used with the mmap syscall in order to retrieve a page of
+memory containing information about the event.
+The PMU driver uses this page to expose to the user the hardware counter's
+index and other necessary data. Using this index enables the user to access the
+PMU registers using the `mrs` instruction.
+
+The userspace access is supported in libperf using the perf_evsel__mmap()
+and perf_evsel__read() functions. See `tools/lib/perf/tests/test-evsel.c`_ for
+an example.
+
+About heterogeneous systems
+---------------------------
+On heterogeneous systems such as big.LITTLE, userspace PMU counter access can
+only be enabled when the tasks are pinned to a homogeneous subset of cores and
+the corresponding PMU instance is opened by specifying the 'type' attribute.
+The use of generic event types is not supported in this case.
+
+Have a look at `tools/perf/arch/arm64/tests/user-events.c`_ for an example. It
+can be run using the perf tool to check that the access to the registers works
+correctly from userspace:
+
+.. code-block:: sh
+
+  perf test -v user
+
+About chained events and 64-bit counters
+----------------------------------------
+Chained events are not supported in conjunction with userspace counter
+access. If a 64-bit counter is requested (attr.config1:0), then
+userspace access must also be requested with attr.config1:1 set. This
+will disable counter chaining. The 'pmc_width' in the user page will
+indicate the actual width of the counter which could be only 32-bits
+depending on event and PMU features.
+
+.. Links
+.. _tools/perf/arch/arm64/tests/user-events.c:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c
-- 
2.27.0


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

  parent reply	other threads:[~2021-03-11  0:09 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-11  0:08 [PATCH v6 00/10] libperf and arm64 userspace counter access support Rob Herring
2021-03-11  0:08 ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 01/10] arm64: pmu: Add function implementation to update event index in userpage Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-30 15:30   ` Will Deacon
2021-03-30 15:30     ` Will Deacon
2021-03-11  0:08 ` [PATCH v6 02/10] arm64: perf: Enable PMU counter direct access for perf event Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-30 11:30   ` Zachary Leaf
2021-03-30 11:30     ` Zachary Leaf
2021-03-30 15:31   ` Will Deacon
2021-03-30 15:31     ` Will Deacon
2021-03-30 17:09     ` Rob Herring
2021-03-30 17:09       ` Rob Herring
2021-03-30 21:08       ` Rob Herring
2021-03-30 21:08         ` Rob Herring
2021-03-31 15:38         ` Will Deacon
2021-03-31 15:38           ` Will Deacon
2021-03-31 17:52           ` Rob Herring
2021-03-31 17:52             ` Rob Herring
2021-04-01  9:04             ` Will Deacon
2021-04-01  9:04               ` Will Deacon
2021-03-31 16:00       ` Will Deacon
2021-03-31 16:00         ` Will Deacon
2021-04-01 19:45         ` Rob Herring
2021-04-01 19:45           ` Rob Herring
2021-04-07 12:44           ` Will Deacon
2021-04-07 12:44             ` Will Deacon
2021-04-08 11:08             ` Mark Rutland
2021-04-08 11:08               ` Mark Rutland
2021-04-08 18:38               ` Rob Herring
2021-04-08 18:38                 ` Rob Herring
2021-04-19 16:14                 ` Will Deacon
2021-04-19 16:14                   ` Will Deacon
2021-04-19 19:00                   ` Rob Herring
2021-04-19 19:00                     ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 03/10] tools/include: Add an initial math64.h Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 04/10] libperf: Add evsel mmap support Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-12 13:58   ` Jiri Olsa
2021-03-12 13:58     ` Jiri Olsa
2021-03-12 14:34     ` Rob Herring
2021-03-12 14:34       ` Rob Herring
2021-03-12 18:29       ` Jiri Olsa
2021-03-12 18:29         ` Jiri Olsa
2021-03-31 22:06         ` Rob Herring
2021-03-31 22:06           ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 05/10] libperf: tests: Add support for verbose printing Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 06/10] libperf: Add support for user space counter access Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-05-04 21:40   ` Ian Rogers
2021-05-04 21:40     ` Ian Rogers
2021-05-05  2:12     ` Rob Herring
2021-05-05  2:12       ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 07/10] libperf: Add arm64 support to perf_mmap__read_self() Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-11  0:08 ` [PATCH v6 08/10] perf: arm64: Add test for userspace counter access on heterogeneous systems Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-15 16:09   ` Masayoshi Mizuma
2021-03-15 16:09     ` Masayoshi Mizuma
2021-03-11  0:08 ` [PATCH v6 09/10] perf: arm64: Add tests for 32-bit and 64-bit counter size userspace access Rob Herring
2021-03-11  0:08   ` Rob Herring
2021-03-11  0:08 ` Rob Herring [this message]
2021-03-11  0:08   ` [PATCH v6 10/10] Documentation: arm64: Document PMU counters access from userspace Rob Herring
2021-03-31 16:00   ` Will Deacon
2021-03-31 16:00     ` Will Deacon
2021-03-30 11:31 ` [PATCH v6 00/10] libperf and arm64 userspace counter access support Zachary Leaf
2021-03-30 11:31   ` Zachary Leaf

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