Messages in this thread | | | Subject | Re: [PATCH v1 1/3] coresight: etm-perf: Correct buffer syncing for snapshot | From | James Clark <> | Date | Tue, 1 Jun 2021 12:53:16 +0300 |
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On 28/05/2021 19:15, Leo Yan wrote: > The perf tool records the Arm CoreSight trace data with snapshot mode > with the option '-S', when receiving USR2 signal, it is observed the > captured trace data size is very varied: from several MBs to ~20MBs. > This can be reproduced with the command: > > perf record -e cs_etm// -S \ > -- dd if=/dev/zero of=/dev/null > /dev/null 2>&1 & > PERFPID=$! > sleep 1 > kill -USR2 $PERFPID > > It's different for only specifying option '-S' than options '-a -S'. If > without option '-a', perf tool creates separate AUX buffers for every > CPU, but the tracer will be enabled only when the profiled program is > scheduled onto the corresponding CPU, this might lead to record very > old trace data when snapshot. > > Let's see below diagram: > snapshot > CPU0: ______###P1###__________________________________________| > CPU1: __________________________###P3###____________###P5###__| > CPU2: ____________________________________###P4###____________| > CPU3: ________________###P2###________________________________V > > In this diagram, the program runs for 5 periods (from P1 to P5), these 5 > periods show the task run on different CPUs, e.g. during P1 period the > program runs on CPU0, and during P2 period the program is migrated to > CPU1, and so on. At the end of P1 period when the program is switched > out from CPU0, the ETR trace data is saved into AUX trace buffer, this > AUX buffer is a dedicated buffer for CPU0's tracer. With the same > logic, P2's trace data is saved into CPU3's tracer buffer, P4's trace > data is saved into CPU2's buffer, P3 and P5's trace data is saved into > CPU1's. Therefore, when snapshot, it saves the trace data from all AUX > ring buffers (in this case, it have total 4 AUX ring buffers) into perf > data file.
Hi Leo,
I was testing out snapshot mode (without your patch) and I noticed that it only ever collects from the last CPU. For example on a 4 core system, the CPU ID of the AUX records and the AUXTRACE buffers is always 3.
This is with systemwide tracing, and running "stress -m 2 -c 2". Is this something that your patch fixes, or am I doing something wrong, or is it just a coincidence?
Here's a snippet of the output:
./perf report -D | grep AUX 0 0 0x200 [0x168]: PERF_RECORD_AUXTRACE_INFO type: 3 0 0 0x152248 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0 ref: 0x75e0bdc44ea1bb65 idx: 3 tid: -1 cpu: 3 3 583600975364460 0x152160 [0x40]: PERF_RECORD_AUX offset: 0x400000 size: 0x400000 flags: 0x2 [O] 0 0 0x55c950 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x400000 ref: 0x6f506d2d02841da4 idx: 3 tid: -1 cpu: 3 3 583602209157460 0x55c908 [0x40]: PERF_RECORD_AUX offset: 0x800000 size: 0x400000 flags: 0x2 [O] 0 0 0x9624d8 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x800000 ref: 0x2d83d30161e1117a idx: 3 tid: -1 cpu: 3 3 583602526365800 0x962490 [0x40]: PERF_RECORD_AUX offset: 0xc00000 size: 0x400000 flags: 0x2 [O] 0 0 0xd65f00 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0xc00000 ref: 0x5013e6e2a3c97c9 idx: 3 tid: -1 cpu: 3 3 583602714310320 0xd65eb8 [0x40]: PERF_RECORD_AUX offset: 0x1000000 size: 0x400000 flags: 0x2 [O] 0 0 0x1169be8 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x1000000 ref: 0x67b37e157f843269 idx: 3 tid: -1 cpu: 3 3 583602874193840 0x1169ba0 [0x40]: PERF_RECORD_AUX offset: 0x1400000 size: 0x400000 flags: 0x2 [O] 0 0 0x156d550 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x1400000 ref: 0x3cb268b926f22d41 idx: 3 tid: -1 cpu: 3 3 583603044203980 0x156d508 [0x40]: PERF_RECORD_AUX offset: 0x1800000 size: 0x400000 flags: 0x2 [O] 0 0 0x1971238 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x1800000 ref: 0x4905e0a21d5d35d7 idx: 3 tid: -1 cpu: 3 3 583603211393440 0x19711f0 [0x40]: PERF_RECORD_AUX offset: 0x1c00000 size: 0x400000 flags: 0x2 [O] 0 0 0x1d747e0 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x1c00000 ref: 0x4f8f48007f7d70e7 idx: 3 tid: -1 cpu: 3 3 583603362643100 0x1d74798 [0x40]: PERF_RECORD_AUX offset: 0x2000000 size: 0x400000 flags: 0x2 [O] 0 0 0x2178368 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x2000000 ref: 0x770d07213be2d29a idx: 3 tid: -1 cpu: 3 3 583603526029900 0x2178320 [0x40]: PERF_RECORD_AUX offset: 0x2400000 size: 0x400000 flags: 0x2 [O] 0 0 0x257bfb0 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x2400000 ref: 0x2e4ed1454815c13e idx: 3 tid: -1 cpu: 3 3 583603687951260 0x257bf68 [0x40]: PERF_RECORD_AUX offset: 0x2800000 size: 0x400000 flags: 0x2 [O] 0 0 0x297fb18 [0x30]: PERF_RECORD_AUXTRACE size: 0x400000 offset: 0x2800000 ref: 0x644eba01d391129 idx: 3 tid: -1 cpu: 3
Thanks James
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