[PATCH V3 0/7] Add interface to expose vpa dtl counters via

[tejas05]

> The pseries Shared Processor Logical Partition(SPLPAR) machines can
> retrieve a log of dispatch and preempt events from the hypervisor
> using data from Disptach Trace Log(DTL) buffer. With this information,
> user can retrieve when and why each dispatch & preempt has occurred.
> The vpa-dtl PMU exposes the Virtual Processor Area(VPA) DTL counters
> via perf.
>
> - Patches 1 to 6 has powerpc PMU driver code changes to capture DTL
>    trace in perf.data. And patch 7 has documentation update.
>
> Infrastructure used
> ===================
>
> The VPA DTL PMU counters do not interrupt on overflow or generate any
> PMI interrupts. Therefore, hrtimer is used to poll the DTL data. The timer
> nterval can be provided by user via sample_period field in nano seconds.
> vpa dtl pmu has one hrtimer added per vpa-dtl pmu thread. DTL (Dispatch
> Trace Log) contains information about dispatch/preempt, enqueue time etc.
> We directly copy the DTL buffer data as part of auxiliary buffer and it
> will be processed later. This will avoid time taken to create samples
> in the kernel space. The PMU driver collecting Dispatch Trace Log (DTL)
> entries makes use of AUX support in perf infrastructure. On the tools side,
> this data is made available as PERF_RECORD_AUXTRACE records.
>
> To corelate each DTL entry with other events across CPU's, an auxtrace_queue
> is created for each CPU. Each auxtrace queue has a array/list of auxtrace buffers.
> All auxtrace queues is maintained in auxtrace heap. The queues are sorted
> based on timestamp. When the different PERF_RECORD_XX records are processed,
> compare the timestamp of perf record with timestamp of top element in the
> auxtrace heap so that DTL events can be co-related with other events
> Process the auxtrace queue if the timestamp of element from heap is
> lower than timestamp from entry in perf record. Sometimes it could happen that
> one buffer is only partially processed. if the timestamp of occurrence of
> another event is more than currently processed element in the queue, it will
> move on to next perf record. So keep track of position of buffer to continue
> processing next time. Update the timestamp of the auxtrace heap with the timestamp
> of last processed entry from the auxtrace buffer.
>
> This infrastructure ensures dispatch trace log entries can be corelated
> and presented along with other events like sched.
>
> With the kernel changes;
>
>    # ls /sys/devices/vpa_dtl/
>    events  format  perf_event_mux_interval_ms  power  subsystem  type  uevent
>
> Thanks
> Athira
>
> Aboorva Devarajan (1):
>    powerpc/time: Expose boot_tb via accessor
>
> Athira Rajeev (4):
>    powerpc/perf/vpa-dtl: Add support to setup and free aux buffer for
>      capturing DTL data
>    powerpc/perf/vpa-dtl: Add support to capture DTL data in aux buffer
>    powerpc/perf/vpa-dtl: Handle the writing of perf record when aux wake
>      up is needed
>    powerpc/perf/vpa-dtl: Add documentation for VPA dispatch trace log PMU
>
> Kajol Jain (2):
>    powerpc/vpa_dtl: Add interface to expose vpa dtl counters via perf
>    docs: ABI: sysfs-bus-event_source-devices-vpa-dtl: Document sysfs
>      event format entries for vpa_dtl pmu
>
>   .../sysfs-bus-event_source-devices-vpa-dtl    |  25 +
>   Documentation/arch/powerpc/index.rst          |   1 +
>   Documentation/arch/powerpc/vpa-dtl.rst        | 156 +++++
>   arch/powerpc/include/asm/time.h               |   4 +
>   arch/powerpc/kernel/time.c                    |   8 +-
>   arch/powerpc/perf/Makefile                    |   2 +-
>   arch/powerpc/perf/vpa-dtl.c                   | 596 ++++++++++++++++++
>   7 files changed, 790 insertions(+), 2 deletions(-)
>   create mode 100644 Documentation/ABI/testing/sysfs-bus-event_source-devices-vpa-dtl
>   create mode 100644 Documentation/arch/powerpc/vpa-dtl.rst
>   create mode 100644 arch/powerpc/perf/vpa-dtl.c
>
Hi Athira,

I have tested the above patchset on the mainline kernel [ 6.17.0-rc6], 
it is working fine. The vpa-dtl pmu is recognizable and the perf record 
report works as expected. Please add the tag below, for the entire series.

Tested-by: Tejas Manhas <tejas05 at linux.ibm.com>

Thanks & Regards,

Tejas