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Fri, 15 Aug 2025 12:17:44 +0000 (GMT) Message-ID: Date: Fri, 15 Aug 2025 17:47:42 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/14] Add interface to expose vpa dtl counters via perf To: Athira Rajeev , acme@kernel.org, jolsa@kernel.org, adrian.hunter@intel.com, maddy@linux.ibm.com, irogers@google.com, namhyung@kernel.org Cc: linux-perf-users@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aboorvad@linux.ibm.com, sshegde@linux.ibm.com, kjain@linux.ibm.com, hbathini@linux.vnet.ibm.com, Aditya.Bodkhe1@ibm.com References: <20250815083407.27953-1-atrajeev@linux.ibm.com> Content-Language: en-GB From: Venkat Rao Bagalkote In-Reply-To: <20250815083407.27953-1-atrajeev@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: oGg2d6HnU7iucdi8M6CrC3E8Zpq29LEn X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODEyMDIyNCBTYWx0ZWRfXwV07VuPdTg7e pHlh0LQ3Phk1mhOUfwji6r7Brx77tlF0QguXfV4jA8dzlobVOxmPk+t9xXNaRBTdpyn/opZa5g3 FK3YDFxdT0+SVQsSqhY16kVO6apG6deJukUC6jSr4fljoW3uGfeyUnYnj9zwxlL+H0dGxsDzb7o glOm1M0lxA8shwFi/Mb+7jy9jb+u386N2tUhzMD5k/vkhTGWkCR0VGwvKAR7kNbLXpMw7f4dAFV lK42rAuBAnsQtsIqsUNQpTgSFMcU+mr459SBaqZE/Wa2LqwSlptLLuYKchSg6uRlJwky2z5MzvQ c1HVixKTVsFfSZ1+NzY4/PHXe2xdoXehAt/MCdE2X55JSZIuimYt2rc5zIl6QFR2ocY8jMTdeF4 YQOPNgUn X-Proofpoint-GUID: ap8HlvcAPM71HJfb5GSvLLeT6Et65eFV X-Authority-Analysis: v=2.4 cv=fLg53Yae c=1 sm=1 tr=0 ts=689f2571 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=2OwXVqhp2XgA:10 a=VnNF1IyMAAAA:8 a=pLHpZT9vZImYFbgc-OIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-15_04,2025-08-14_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 clxscore=1015 spamscore=0 priorityscore=1501 impostorscore=0 phishscore=0 malwarescore=0 bulkscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2508120224 On 15/08/25 2:03 pm, Athira Rajeev 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 14 has documentation update. > - Patch 7 to 13 is perf tools side code changes to enable perf > report/script on perf.data file > > 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. > > vpa-dtl PMU example usage > > # ls /sys/devices/vpa_dtl/ > events format perf_event_mux_interval_ms power subsystem type uevent > > > To capture the DTL data using perf record: > > # ./perf record -a -e sched:*,vpa_dtl/dtl_all/ -c 1000000000 sleep 1 > > The result can be interpreted using perf report. Snippet of perf report -D: > > # ./perf report -D > > There are different PERF_RECORD_XX records. In that records corresponding to > auxtrace buffers includes: > > 1. PERF_RECORD_AUX > Conveys that new data is available in AUX area > > 2. PERF_RECORD_AUXTRACE_INFO > Describes offset and size of auxtrace data in the buffers > > 3. PERF_RECORD_AUXTRACE > This is the record that defines the auxtrace data which here in case of > vpa-dtl pmu is dispatch trace log data. > > Snippet from perf report -D showing the PERF_RECORD_AUXTRACE dump > > 0 0 0x39b10 [0x30]: PERF_RECORD_AUXTRACE size: 0x690 offset: 0 ref: 0 idx: 0 tid: -1 cpu: 0 > . > . ... VPA DTL PMU data: size 1680 bytes, entries is 35 > . 00000000: boot_tb: 21349649546353231, tb_freq: 512000000 > . 00000030: dispatch_reason:decrementer interrupt, preempt_reason:H_CEDE, enqueue_to_dispatch_time:7064, ready_to_enqueue_time:187, waiting_to_ready_time:6611773 > . 00000060: dispatch_reason:priv doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:146, ready_to_enqueue_time:0, waiting_to_ready_time:15359437 > . 00000090: dispatch_reason:decrementer interrupt, preempt_reason:H_CEDE, enqueue_to_dispatch_time:4868, ready_to_enqueue_time:232, waiting_to_ready_time:5100709 > . 000000c0: dispatch_reason:priv doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:179, ready_to_enqueue_time:0, waiting_to_ready_time:30714243 > . 000000f0: dispatch_reason:priv doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:197, ready_to_enqueue_time:0, waiting_to_ready_time:15350648 > . 00000120: dispatch_reason:priv doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:213, ready_to_enqueue_time:0, waiting_to_ready_time:15353446 > . 00000150: dispatch_reason:priv doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:212, ready_to_enqueue_time:0, waiting_to_ready_time:15355126 > . 00000180: dispatch_reason:decrementer interrupt, preempt_reason:H_CEDE, enqueue_to_dispatch_time:6368, ready_to_enqueue_time:164, waiting_to_ready_time:5104665 > > Above is representation of dtl entry of below format: > > struct dtl_entry { > u8 dispatch_reason; > u8 preempt_reason; > u16 processor_id; > u32 enqueue_to_dispatch_time; > u32 ready_to_enqueue_time; > u32 waiting_to_ready_time; > u64 timebase; > u64 fault_addr; > u64 srr0; > u64 srr1; > }; > > First two fields represent the dispatch reason and preempt reason. The post > procecssing of PERF_RECORD_AUXTRACE records will translate to meaninful data > for user to consume. > > Visualize the dispatch trace log entries with perf report: > > # ./perf record -a -e sched:*,vpa_dtl/dtl_all/ -c 1000000000 sleep 1 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.300 MB perf.data ] > > # ./perf report > # Samples: 321 of event 'vpa-dtl' > # Event count (approx.): 321 > # > # Children Self Command Shared Object Symbol > # ........ ........ ....... ................. .............................. > # > 100.00% 100.00% swapper [kernel.kallsyms] [k] plpar_hcall_norets_notrace > > Visualize the dispatch trace log entries with perf script: > > # ./perf script > perf 13322 [002] 233.835807: sched:sched_switch: perf:13322 [120] R ==> migration/2:27 [0] > migration/2 27 [002] 233.835811: sched:sched_migrate_task: comm=perf pid=13322 prio=120 orig_cpu=2 dest_cpu=3 > migration/2 27 [002] 233.835818: sched:sched_stat_runtime: comm=migration/2 pid=27 runtime=9214 [ns] > migration/2 27 [002] 233.835819: sched:sched_switch: migration/2:27 [0] S ==> swapper/2:0 [120] > swapper 0 [002] 233.835822: vpa-dtl: timebase: 338954486062657 dispatch_reason:decrementer_interrupt, preempt_reason:H_CEDE, enqueue_to_dispatch_time:435, ready_to_enqueue_time:0, waiting_to_ready_time:34775058, processor_id: 202 c0000000000f8094 plpar_hcall_norets_notrace+0x18 ([kernel.kallsyms]) > swapper 0 [001] 233.835886: vpa-dtl: timebase: 338954486095398 dispatch_reason:priv_doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:542, ready_to_enqueue_time:0, waiting_to_ready_time:1245360, processor_id: 201 c0000000000f8094 plpar_hcall_norets_notrace+0x18 ([kernel.kallsyms]) > > Aboorva Devarajan (1): > powerpc/time: Expose boot_tb via accessor > > Athira Rajeev (11): > 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 > tools/perf: Add basic CONFIG_AUXTRACE support for VPA pmu on powerpc > tools/perf: process auxtrace events and display in perf report -D > tools/perf: Add event name as vpa-dtl of PERF_TYPE_SYNTH type to > present DTL samples > tools/perf: Allocate and setup aux buffer queue to help co-relate with > other events across CPU's > tools/perf: Process the DTL entries in queue and deliver samples > tools/perf: Add support for printing synth event details via default > callback > tools/perf: Enable perf script to present the DTL entries > 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 | 155 ++++ > arch/powerpc/include/asm/time.h | 2 + > arch/powerpc/kernel/time.c | 7 +- > arch/powerpc/perf/Makefile | 2 +- > arch/powerpc/perf/vpa-dtl.c | 605 ++++++++++++++ > tools/perf/arch/powerpc/util/Build | 1 + > tools/perf/arch/powerpc/util/auxtrace.c | 122 +++ > tools/perf/builtin-script.c | 26 + > tools/perf/util/Build | 1 + > tools/perf/util/auxtrace.c | 4 + > tools/perf/util/auxtrace.h | 1 + > tools/perf/util/event.h | 1 + > tools/perf/util/powerpc-vpadtl.c | 756 ++++++++++++++++++ > tools/perf/util/powerpc-vpadtl.h | 45 ++ > 16 files changed, 1752 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 > create mode 100644 tools/perf/arch/powerpc/util/auxtrace.c > create mode 100644 tools/perf/util/powerpc-vpadtl.c > create mode 100644 tools/perf/util/powerpc-vpadtl.h > Tested this patchset by applying on top of mainline kernel, and its working as expected. Hence for the entire series, please add below tag. Tested-by: Venkat Rao Bagalkote Regards, Venkat.