Re: [PATCH v5 0/8] perf record --off-cpu: Dump off-cpu samples directly

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Sep 27, 2024 at 11:53:32AM -0700, Howard Chu wrote:
> 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

Thanks, I'll try to review and test this early next week, and check on
bisectability issues as you mentioned privately.

Thanks!

- Arnaldo
 
> 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 (8):
>   perf evsel: Set off-cpu BPF output to system-wide
>   perf record --off-cpu: Add --off-cpu-thresh
>   perf record --off-cpu: Parse offcpu-time event
>   perf record off-cpu: Dump direct off-cpu samples in BPF
>   perf record --off-cpu: Dump total off-cpu time at the end.
>   perf evsel: Delete unnecessary = 0
>   perf record --off-cpu: Parse BPF output embedded data
>   perf test: Add direct off-cpu dumping test
> 
>  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 |  29 ++++
>  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           | 174 +++++++++++++++---------
>  tools/perf/util/bpf_skel/off_cpu.bpf.c  | 123 +++++++++++++++++
>  tools/perf/util/evsel.c                 |  47 ++++---
>  tools/perf/util/evsel.h                 |   6 +
>  tools/perf/util/off_cpu.h               |  10 +-
>  tools/perf/util/record.h                |   1 +
>  tools/perf/util/session.c               |  12 +-
>  14 files changed, 359 insertions(+), 92 deletions(-)
>  create mode 100644 tools/perf/tests/workloads/offcpu.c
> 
> -- 
> 2.43.0