[v8,5/5] docs: perf: Minimal introduction the the CXL PMU device and driver

Commit Message

Jonathan Cameron May 31, 2023, 11 a.m. UTC

Very basic introduction to the device and the current driver support
provided. I expect to expand on this in future versions of this patch
set.

Reviewed-by: Dave Jiang <[e-mail]>
Reviewed-by: Kan Liang <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

---
v7
- Added explict -a to command line examples to make it obvious the
  counters apply only to all CPUs (no per thread or per process).
---
 Documentation/admin-guide/perf/cxl.rst   | 68 ++++++++++++++++++++++++
 Documentation/admin-guide/perf/index.rst |  1 +
 MAINTAINERS                              |  1 +
 3 files changed, 70 insertions(+)

Patch

diff --git a/Documentation/admin-guide/perf/cxl.rst b/Documentation/admin-guide/perf/cxl.rst
new file mode 100644
index 000000000000..9233ea0d0b10
--- /dev/null
+++ b/Documentation/admin-guide/perf/cxl.rst
@@ -0,0 +1,68 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================
+CXL Performance Monitoring Unit (CPMU)
+======================================
+
+The CXL rev 3.0 specification provides a definition of CXL Performance
+Monitoring Unit in section 13.2: Performance Monitoring.
+
+CXL components (e.g. Root Port, Switch Upstream Port, End Point) may have
+any number of CPMU instances. CPMU capabilities are fully discoverable from
+the devices. The specification provides event definitions for all CXL protocol
+message types and a set of additional events for things commonly counted on
+CXL devices (e.g. DRAM events).
+
+CPMU driver
+===========
+
+The CPMU driver registers a perf PMU with the name pmu_mem<X>.<Y> on the CXL bus
+representing the Yth CPMU for memX.
+
+    /sys/bus/cxl/device/pmu_mem<X>.<Y>
+
+The associated PMU is registered as
+
+   /sys/bus/event_sources/devices/cxl_pmu_mem<X>.<Y>
+
+In common with other CXL bus devices, the id has no specific meaning and the
+relationship to specific CXL device should be established via the device parent
+of the device on the CXL bus.
+
+PMU driver provides description of available events and filter options in sysfs.
+
+The "format" directory describes all formats of the config (event vendor id,
+group id and mask) config1 (threshold, filter enables) and config2 (filter
+parameters) fields of the perf_event_attr structure.  The "events" directory
+describes all documented events show in perf list.
+
+The events shown in perf list are the most fine grained events with a single
+bit of the event mask set. More general events may be enable by setting
+multiple mask bits in config. For example, all Device to Host Read Requests
+may be captured on a single counter by setting the bits for all of
+
+* d2h_req_rdcurr
+* d2h_req_rdown
+* d2h_req_rdshared
+* d2h_req_rdany
+* d2h_req_rdownnodata
+
+Example of usage::
+
+  $#perf list
+  cxl_pmu_mem0.0/clock_ticks/                        [Kernel PMU event]
+  cxl_pmu_mem0.0/d2h_req_rdshared/                   [Kernel PMU event]
+  cxl_pmu_mem0.0/h2d_req_snpcur/                     [Kernel PMU event]
+  cxl_pmu_mem0.0/h2d_req_snpdata/                    [Kernel PMU event]
+  cxl_pmu_mem0.0/h2d_req_snpinv/                     [Kernel PMU event]
+  -----------------------------------------------------------
+
+  $# perf stat -a -e cxl_pmu_mem0.0/clock_ticks/ -e cxl_pmu_mem0.0/d2h_req_rdshared/
+
+Vendor specific events may also be available and if so can be used via
+
+  $# perf stat -a -e cxl_pmu_mem0.0/vid=VID,gid=GID,mask=MASK/
+
+The driver does not support sampling so "perf record" is unsupported.
+It only supports system-wide counting so attaching to a task is
+unsupported.
diff --git a/Documentation/admin-guide/perf/index.rst b/Documentation/admin-guide/perf/index.rst
index 9de64a40adab..f60be04e4e33 100644
--- a/Documentation/admin-guide/perf/index.rst
+++ b/Documentation/admin-guide/perf/index.rst
@@ -21,3 +21,4 @@  Performance monitor support
    alibaba_pmu
    nvidia-pmu
    meson-ddr-pmu
+   cxl
diff --git a/MAINTAINERS b/MAINTAINERS
index 976b3e982d3a..5388b5c2e5bb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5195,6 +5195,7 @@  COMPUTE EXPRESS LINK PMU (CPMU)
 M:	Jonathan Cameron <[e-mail]>
 L:	[e-mail]
 S:	Maintained
+F:	Documentation/admin-guide/perf/cxl.rst
 F:	drivers/perf/cxl_pmu.c
 
 CONEXANT ACCESSRUNNER USB DRIVER