> On 17 Sep 2025, at 2:29 PM, tejas05 <teja...@linux.ibm.com> wrote:
>
>> 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 <teja...@linux.ibm.com>
>
> Thanks & Regards,
>
> Tejas
Thanks Tejas and Venkat for testing the patch series
Athira
