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Without the '--sort-events' flag, perf trace doesn't receive and process
events based on their arrival time, thus PERF_RECORD_COMM event that
assigns the correct comm to a PID, may be delivered and processed after
regular samples, causing trace outputs not having a 'comm', e.g.
'mv', instead, having the default PID placeholder, e.g. ':14514'.
Hopefully this answers Namhyung's question in [1].
You can simply justify the statement with this diff: [2].
Now, simply run this command multiple times:
$ touch /tmp/file1 && sudo /tmp/perf trace -e renameat* -- mv /tmp/file1 /tmp/file2 && rm -f /tmp/file2
And you should see two types of results:
$ touch /tmp/file1 && sudo /tmp/perf trace -e renameat* -- mv /tmp/file1 /tmp/file2 && rm -f /tmp/file2
[debug] deliver
[debug] machine__process_comm_event
[OVERRIDE] old :1221169 new mv str mv
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
0.000 ( 0.013 ms): mv/1221169 renameat2(olddfd: CWD, oldname: "/tmp/file1", newdfd: CWD, newname: "/tmp/file2", flags: NOREPLACE) = 0
[debug] deliver
$ touch /tmp/file1 && sudo /tmp/perf trace -e renameat* -- mv /tmp/file1 /tmp/file2 && rm -f /tmp/file2
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
[debug] deliver
0.000 ( 0.014 ms): :1221398/1221398 renameat2(olddfd: CWD, oldname: "/tmp/file1", newdfd: CWD, newname: "/tmp/file2", flags: NOREPLACE) = 0
[debug] deliver
[debug] deliver
[debug] machine__process_comm_event
[OVERRIDE] old :1221398 new mv str mv
[debug] deliver
[debug] deliver
[debug] deliver
Anyway, use --sort-events in BTF general tests to avoid :PID, a comm is
preferred.
[1]: https://lore.kernel.org/linux-perf-users/Z_AeswETE5xLcPT8@google.com/
[2]:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.