Message-ID: <CAH0uvogp4GB6ZkB=79wCNVtOhsGw-aofzGmW6nPc--b=g-D9OQ@mail.gmail.com>
Date: Mon, 16 Dec 2024 12:49:26 -0800
From: Howard Chu <howardchu95@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: acme@...nel.org, mark.rutland@....com, alexander.shishkin@...ux.intel.com, 
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com, 
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 00/10] perf record --off-cpu: Dump off-cpu samples directly

Hello Namhyung,

On Mon, Dec 16, 2024 at 12:11 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> 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.

I think you misspelled 'procrastination' :). All jokes aside, thank
you for the reviews—it’s much harder on your side.

Thanks,
Howard

>
> Reviewed-by: Namhyung Kim <namhyung@...nel.org>
>
> Thanks,
> Namhyung

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