Re: [PATCH v3 1/2] perf/docs: Add info on AMD raw event encoding

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Sun, Nov 28, 2021 at 05:38:17PM +0100, Jiri Olsa escreveu:
> On Tue, Nov 23, 2021 at 02:16:12PM +0530, Sandipan Das wrote:
> > AMD processors have events with event select codes and unit
> > masks larger than a byte. The core PMU, for example, uses
> > 12-bit event select codes split between bits 0-7 and 32-35
> > of the PERF_CTL MSRs as can be seen from
> > /sys/bus/event_sources/devices/cpu/format/*.
> > 
> > The Processor Programming Reference (PPR) lists the event
> > codes as unified 12-bit hexadecimal values instead and the
> > split between the bits is not apparent to someone who is
> > not aware of the layout of the PERF_CTL MSRs.
> > 
> > 8-bit event select codes continue to work as the layout
> > matches that of the PERF_CTL MSRs i.e. bits 0-7 for event
> > select and 8-15 for unit mask.
> > 
> > This adds more details in the perf man pages about using
> > /sys/bus/event_sources/devices/*/format/* for determining
> > the correct raw event encoding scheme.
> > 
> > E.g. the "op_cache_hit_miss.op_cache_hit" event with code
> > 0x28f and umask 0x03 can be programmed using its symbolic
> > name as:
> > 
> >   $ sudo perf --debug perf-event-open stat -e op_cache_hit_miss.op_cache_hit sleep 1
> >   ------------------------------------------------------------
> >   perf_event_attr:
> >     type                             4
> >     size                             128
> >     config                           0x20000038f
> >     sample_type                      IDENTIFIER
> >     read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
> >     disabled                         1
> >     inherit                          1
> >     enable_on_exec                   1
> >     exclude_guest                    1
> >   ------------------------------------------------------------
> >   [...]
> > 
> > One might use a simple eventsel+umask combination based on
> > what the current man pages say and incorrectly program the
> > event as:
> > 
> >   $ sudo perf --debug perf-event-open stat -e r0328f sleep 1
> >   ------------------------------------------------------------
> >   perf_event_attr:
> >     type                             4
> >     size                             128
> >     config                           0x328f
> >     sample_type                      IDENTIFIER
> >     read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
> >     disabled                         1
> >     inherit                          1
> >     enable_on_exec                   1
> >     exclude_guest                    1
> >   ------------------------------------------------------------
> >   [...]
> > 
> > When it should have been based on the format from sysfs:
> > 
> >   $ cat /sys/bus/event_source/devices/cpu/format/event
> >   config:0-7,32-35
> > 
> >   $ sudo perf --debug perf-event-open stat -e r20000038f sleep 1
> >   ------------------------------------------------------------
> >   perf_event_attr:
> >     type                             4
> >     size                             128
> >     config                           0x20000038f
> >     sample_type                      IDENTIFIER
> >     read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
> >     disabled                         1
> >     inherit                          1
> >     enable_on_exec                   1
> >     exclude_guest                    1
> >   ------------------------------------------------------------
> >   [...]
> > 
> > Signed-off-by: Sandipan Das <sandipan.das@amd.com>
> > ---
> > v1: https://lore.kernel.org/linux-perf-users/20211119111234.170726-1-sandipan.das@amd.com/
> > v2: https://lore.kernel.org/linux-perf-users/20211123065104.236717-1-sandipan.das@amd.com/
> > 
> > v3:
> > - Mention why simple eventsel+umask combinations will not
> >   work in the commit message.
> 
> for both patches:
> 
> Acked-by: Jiri Olsa <jolsa@redhat.com>

Thanks, applied.

- Arnaldo