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
