Messages in this thread Patch in this message | | | From | Jonathan Cameron <> | Subject | [RFC PATCH 4/4] docs: perf: Minimal introduction the the CXL PMU device and driver. | Date | Fri, 12 Aug 2022 16:12:14 +0100 |
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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.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
-- RFC: - I'll post separately about this shortly, but it seems very odd to me that there is no way to assign a parent to an event_sources device. As a result we get the messy approach of playing match the name to figure out what the CPMU instance is connected to. --- Documentation/admin-guide/perf/cxl.rst | 60 ++++++++++++++++++++++++ Documentation/admin-guide/perf/index.rst | 1 + 2 files changed, 61 insertions(+)
diff --git a/Documentation/admin-guide/perf/cxl.rst b/Documentation/admin-guide/perf/cxl.rst new file mode 100644 index 000000000000..6ffc057591fb --- /dev/null +++ b/Documentation/admin-guide/perf/cxl.rst @@ -0,0 +1,60 @@ +====================================== +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 register a perf PMU with the name cpmu<id> on the CXL bus. + + /sys/bus/cxl/device/cpmu<id> + +The associated PMU is registered as + + /sys/bus/event_sources/devices/cpmu<id> + +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 + cpmu0/clock_ticks/ [Kernel PMU event] + cpmu0/d2h_req_itomwr/ [Kernel PMU event] + cpmu0/d2h_req_rdany/ [Kernel PMU event] + cpmu0/d2h_req_rdcurr/ [Kernel PMU event] + ----------------------------------------------------------- + + $# perf stat -e cpmu0/clock_ticks/ -e cpmu0/d2h_req_itowrm/ + +The driver does not support sampling. So "perf record" and attaching to +a task are unsupported. + diff --git a/Documentation/admin-guide/perf/index.rst b/Documentation/admin-guide/perf/index.rst index 69b23f087c05..ff1ac52c37fb 100644 --- a/Documentation/admin-guide/perf/index.rst +++ b/Documentation/admin-guide/perf/index.rst @@ -17,3 +17,4 @@ Performance monitor support xgene-pmu arm_dsu_pmu thunderx2-pmu + cxl -- 2.32.0
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