Re: [PATCH v14 00/10] perf record --off-cpu: Dump off-cpu samples directly

[Namhyung Kim <namhyung@kernel.org>]

On Sun, Dec 15, 2024 at 10:12:10AM -0800, Howard Chu wrote:
> Changes in v14:
>  - Change the internal off_cpu_thresh_us to off_cpu_thresh_ns, i.e. use
>    nsec instead of usec
> 
> Changes in v13:
>  - Move the definition of 'off_cpu_thresh_ns' to the same commit as
>    dumping off-cpu samples in BPF, and give off_cpu_thresh_ns a default
>    value before the --off-cpu-thresh option is parsed.
> 
> Changes in v12:
>  - Restore patches' bisectability, because the ordering of patches has
>    changed.
>  - Change 'us = ms * 1000' to 'us = ms * USEC_PER_MSEC'
> 
> Changes in v11:
>  - Modify the options used in the off-cpu tests, as I changed the unit
>    of the off-cpu threshold to milliseconds.
> 
> Changes in v10:
>  - Move the commit "perf record --off-cpu: Add --off-cpu-thresh option"
>    to where the direct sample feature is completed.
>  - Make --off-cpu-thresh use milliseconds as the unit.
> 
> Changes in v9:
>  - Add documentation for the new option '--off-cpu-thresh', and include
>    an example of its usage in the commit message
>  - Set inherit in evsel__config() to prevent future modifications
>  - Support off-cpu sample data collected by perf before this patch series
> 
> Changes in v8:
>  - Make this series bisectable
>  - Rename off_cpu_thresh to off_cpu_thresh_us and offcpu_thresh (in BPF)
>    to offcpu_thresh_ns for clarity
>  - Add commit messages to 'perf evsel: Expose evsel__is_offcpu_event()
>    for future use' commit
>  - Correct spelling mistakes in the commit message (s/is should be/should be/)
>  - Add kernel-doc comments to off_cpu_dump(), and comments to the empty
>    if block
>  - Add some comments to off-cpu test
>  - Delete an unused variable 'timestamp' in off_cpu_dump()
> 
> Changes in v7:
>  - Make off-cpu event system-wide
>  - Use strtoull instead of strtoul
>  - Delete unused variable such as sample_id, and sample_type
>  - Use i as index to update BPF perf_event map
>  - MAX_OFFCPU_LEN 128 is too big, make it smaller.
>  - Delete some bound check as it's always guaranteed
>  - Do not set ip_pos in BPF
>  - Add a new field for storing stack traces in the tstamp map
>  - Dump the off-cpu sample directly or save it in the off_cpu map, not both
>  - Delete the sample_type_off_cpu check
>  - Use __set_off_cpu_sample() to parse samples instead of a two-pass parsing
> 
> Changes in v6:
>  - Make patches bisectable
> 
> Changes in v5:
>  - Delete unnecessary copy in BPF program
>  - Remove sample_embed from perf header, hard code off-cpu stuff instead
>  - Move evsel__is_offcpu_event() to evsel.h
>  - Minor changes to the test
>  - Edit some comments
> 
> Changes in v4:
>  - Minimize the size of data output by perf_event_output()
>  - Keep only one off-cpu event
>  - Change off-cpu threshold's unit to microseconds
>  - Set a default off-cpu threshold
>  - Print the correct error message for the field 'embed' in perf data header
> 
> Changes in v3:
>  - Add off-cpu-thresh argument
>  - Process direct off-cpu samples in post
> 
> Changes in v2:
>  - Remove unnecessary comments.
>  - Rename function off_cpu_change_type to off_cpu_prepare_parse
> 
> v1:
> 
> As mentioned in: https://bugzilla.kernel.org/show_bug.cgi?id=207323
> 
> Currently, off-cpu samples are dumped when perf record is exiting. This
> results in off-cpu samples being after the regular samples. This patch
> series makes possible dumping off-cpu samples on-the-fly, directly into
> perf ring buffer. And it dispatches those samples to the correct format
> for perf.data consumers.
> 
> Before:
> ```
>      migration/0      21 [000] 27981.041319: 2944637851    cycles:P:  ffffffff90d2e8aa record_times+0xa ([kernel.kallsyms])
>             perf  770116 [001] 27981.041375:          1    cycles:P:  ffffffff90ee4960 event_function+0xf0 ([kernel.kallsyms])
>             perf  770116 [001] 27981.041377:          1    cycles:P:  ffffffff90c184b1 intel_bts_enable_local+0x31 ([kernel.kallsyms])
>             perf  770116 [001] 27981.041379:      51611    cycles:P:  ffffffff91a160b0 native_sched_clock+0x30 ([kernel.kallsyms])
>      migration/1      26 [001] 27981.041400: 4227682775    cycles:P:  ffffffff90d06a74 wakeup_preempt+0x44 ([kernel.kallsyms])
>      migration/2      32 [002] 27981.041477: 4159401534    cycles:P:  ffffffff90d11993 update_load_avg+0x63 ([kernel.kallsyms])
> 
> sshd  708098 [000] 18446744069.414584:     286392 offcpu-time: 
> 	    79a864f1c8bb ppoll+0x4b (/usr/lib/libc.so.6)
> 	    585690935cca [unknown] (/usr/bin/sshd)
> ```
> 
> After:
> ```
>             perf  774767 [003] 28178.033444:        497           cycles:P:  ffffffff91a160c3 native_sched_clock+0x43 ([kernel.kallsyms])
>             perf  774767 [003] 28178.033445:     399440           cycles:P:  ffffffff91c01f8d nmi_restore+0x25 ([kernel.kallsyms])
>          swapper       0 [001] 28178.036639:  376650973           cycles:P:  ffffffff91a1ae99 intel_idle+0x59 ([kernel.kallsyms])
>          swapper       0 [003] 28178.182921:  348779378           cycles:P:  ffffffff91a1ae99 intel_idle+0x59 ([kernel.kallsyms])
>     blueman-tray    1355 [000] 28178.627906:  100184571 offcpu-time: 
> 	    7528eef1c39d __poll+0x4d (/usr/lib/libc.so.6)
> 	    7528edf7d8fd [unknown] (/usr/lib/libglib-2.0.so.0.8000.2)
> 	    7528edf1af95 g_main_context_iteration+0x35 (/usr/lib/libglib-2.0.so.0.8000.2)
> 	    7528eda4ab86 g_application_run+0x1f6 (/usr/lib/libgio-2.0.so.0.8000.2)
> 	    7528ee6aa596 [unknown] (/usr/lib/libffi.so.8.1.4)
> 	    7fff24e862d8 [unknown] ([unknown])
> 
> 
>     blueman-tray    1355 [000] 28178.728137:  100187539 offcpu-time: 
> 	    7528eef1c39d __poll+0x4d (/usr/lib/libc.so.6)
> 	    7528edf7d8fd [unknown] (/usr/lib/libglib-2.0.so.0.8000.2)
> 	    7528edf1af95 g_main_context_iteration+0x35 (/usr/lib/libglib-2.0.so.0.8000.2)
> 	    7528eda4ab86 g_application_run+0x1f6 (/usr/lib/libgio-2.0.so.0.8000.2)
> 	    7528ee6aa596 [unknown] (/usr/lib/libffi.so.8.1.4)
> 	    7fff24e862d8 [unknown] ([unknown])
> 
> 
>          swapper       0 [000] 28178.463253:  195945410           cycles:P:  ffffffff91a1ae99 intel_idle+0x59 ([kernel.kallsyms])
>      dbus-broker     412 [002] 28178.464855:  376737008           cycles:P:  ffffffff91c000a0 entry_SYSCALL_64+0x20 ([kernel.kallsyms])
> ```
> 
> Howard Chu (10):
>   perf evsel: Expose evsel__is_offcpu_event() for future use
>   perf record --off-cpu: Parse off-cpu event
>   perf record --off-cpu: Preparation of off-cpu BPF program
>   perf record --off-cpu: Dump off-cpu samples in BPF
>   perf evsel: Assemble offcpu samples
>   perf record --off-cpu: Disable perf_event's callchain collection
>   perf script: Display off-cpu samples correctly
>   perf record --off-cpu: Dump the remaining samples in BPF's stack trace
>     map
>   perf record --off-cpu: Add --off-cpu-thresh option
>   perf test: Add direct off-cpu test

Thanks for your work and the persistence.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung

> 
>  tools/perf/Documentation/perf-record.txt |   9 ++
>  tools/perf/builtin-record.c              |  26 +++++
>  tools/perf/builtin-script.c              |   4 +-
>  tools/perf/tests/builtin-test.c          |   1 +
>  tools/perf/tests/shell/record_offcpu.sh  |  35 ++++++-
>  tools/perf/tests/tests.h                 |   1 +
>  tools/perf/tests/workloads/Build         |   1 +
>  tools/perf/tests/workloads/offcpu.c      |  16 +++
>  tools/perf/util/bpf_off_cpu.c            | 118 ++++++++++++++---------
>  tools/perf/util/bpf_skel/off_cpu.bpf.c   |  97 ++++++++++++++++++-
>  tools/perf/util/evsel.c                  |  41 +++++++-
>  tools/perf/util/evsel.h                  |   2 +
>  tools/perf/util/off_cpu.h                |   3 +-
>  tools/perf/util/record.h                 |   1 +
>  14 files changed, 297 insertions(+), 58 deletions(-)
>  create mode 100644 tools/perf/tests/workloads/offcpu.c
> 
> -- 
> 2.43.0
>