Re: [PATCH v4 5/5] docs: perf: Minimal introduction the the CXL PMU device and driver

[Jonathan Cameron]

On Mon, 3 Apr 2023 13:45:52 -0400
"Liang, Kan" <kan.liang@xxxxxxxxxxxxxxx> wrote:

> On 2023-03-30 12:45 p.m., 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.
> > 
> > Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> > 
> > --
> > v4: No change
> > ---
> >  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.  
> 
> The PMU only supports system-wide counting. That's the reason it doesn't
> support per-task profiling. Not because of missing sampling.

Ah. I've managed to fuse two different conditions. I'll break them apart for
v5.

Thanks,

Jonathan

> 
> Thanks,
> Kan
> > 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  
>