From: Mateusz Guzik <mjguzik@gmail.com>
To: libc-alpha@sourceware.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Adhemerval Zanella <adhemerval.zanella@linaro.org>
Subject: fstat(2) penalized by using newfstatat(6, "", buf, AT_EMPTY_PATH)
Date: Mon, 4 Sep 2023 11:55:37 +0200 [thread overview]
Message-ID: <CAGudoHG83bsjmsy9nvmqUGrSORRdnu0D8tQDRq=qm8+WWT00Eg@mail.gmail.com> (raw)
Commit 4d97cc8cf3da ("io: Remove xstat implementations") reimplemented
fstat entry point on top of newfstatat (as opposed to newfstat).
This comes with a significant performance penalty as it induces a lot
of work on kernel side to handle the path, which is additionally
slowed down on x86-64 due to SMAP handling.
Here are sample results from calling newfstatat vs newfstat on Sapphire Rapids:
newfstatat 5088199
newfstat 8540383 (+67%)
Are there any problems switching it back to newfstat at least for x86-64?
If you want to bench yourself you can grab will-it-scale +
https://github.com/antonblanchard/will-it-scale/pull/35/files + patch
up one of the testcases to call newfstat directly: int error =
syscall(5, fd, &sb);
Note if you bench yourself and have a CPU significantly impacted by
mitigations (e.g., meltdown) the difference may be very small in your
setup.
--
Mateusz Guzik <mjguzik gmail.com>
next reply other threads:[~2023-09-04 9:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-04 9:55 Mateusz Guzik [this message]
2023-09-04 10:08 ` Andreas Schwab
2023-09-04 10:11 ` Mateusz Guzik
2023-09-05 13:01 ` Adhemerval Zanella Netto
2023-09-05 13:14 ` Mateusz Guzik
2023-09-05 17:28 ` Adhemerval Zanella Netto
2023-09-05 17:45 ` Linus Torvalds
2023-09-05 18:22 ` Adhemerval Zanella Netto
2023-09-05 19:16 ` Adhemerval Zanella Netto
2023-09-05 19:21 ` Linus Torvalds
2023-09-05 21:42 ` Rich Felker
2023-09-05 21:46 ` Mateusz Guzik
2023-09-05 17:29 ` Linus Torvalds
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