> On 15 Sep 2025, at 3:59 PM, Athira Rajeev <atraj...@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
>
> --
> 2.47.1
>
Tested this patch set by applying on top of today’s mainline kernel and its
working as expected.
Please add below tag for the patch set.
Tested-by: Venkat Rao Bagalkote <venka...@linux.ibm.com>
Regards,
Venkat.
