Le 15/09/2025 à 12:29, Athira Rajeev a écrit :
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
What is the difference between this version of the series and the V2 sent 3 hours ago ?
Christophe
