linux-kernel - Re: [PATCH 4/4] docs: perf: Minimal introduction the the CXL PMU device and driver.

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Date:   Fri, 3 Mar 2023 11:34:37 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-cxl@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, will@...nel.org, dan.j.williams@...el.com,
        bwidawsk@...nel.org, ira.weiny@...el.com, vishal.l.verma@...el.com,
        alison.schofield@...el.com, linuxarm@...wei.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] docs: perf: Minimal introduction the the CXL PMU
 device and driver.



On 3/3/23 10:50 AM, Jonathan Cameron wrote:
> 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@...wei.com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>

> 
> --
> v1:
> - Add docs for how to use a Vendor Defined Counter.
> 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.

Would it be too awkward to encode the parent name into the cpmu name?

> ---
>   Documentation/admin-guide/perf/cxl.rst   | 65 ++++++++++++++++++++++++
>   Documentation/admin-guide/perf/index.rst |  1 +
>   2 files changed, 66 insertions(+)
> 
> diff --git a/Documentation/admin-guide/perf/cxl.rst b/Documentation/admin-guide/perf/cxl.rst
> new file mode 100644
> index 000000000000..46235dff4b21
> --- /dev/null
> +++ b/Documentation/admin-guide/perf/cxl.rst
> @@ -0,0 +1,65 @@
> +.. 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 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/
> +
> +Vendor specific events may also be available and if so can be used via
> +
> +  $# perf stat -e cpmu0/vid=VID,gid=GID,mask=MASK/
> +
> +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 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