public inbox for libc-alpha@sourceware.org
 help / color / mirror / Atom feed
From: Florian Weimer <fweimer@redhat.com>
To: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
Cc: Adhemerval Zanella <adhemerval.zanella@linaro.org>,
	crrodriguez@opensuse.org
Subject: Re: [PATCH 2/4] linux: Use sched_getaffinity for __get_nprocs (BZ #27645)
Date: Tue, 27 Apr 2021 17:38:25 +0200	[thread overview]
Message-ID: <87tunrloum.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20210329182520.323665-2-adhemerval.zanella@linaro.org> (Adhemerval Zanella via Libc-alpha's message of "Mon, 29 Mar 2021 15:25:18 -0300")

* Adhemerval Zanella via Libc-alpha:

> Both the sysfs and procfs parsing (through GET_NPROCS_PARSER) are
> removed in favor the syscall.  The initial scratch buffer should
> fit to most of the common usage (1024 bytes with maps to 8192 CPUs).

The code changes look okay to me.

I don't know if it is safe to ever return 1, though, because some
container hosts return just one bit in the affinity mask, but will still
schedule threads on different CPUs, so the single-processor
synchronization that is normally implied by a CPU count of 1 isn't
guaranteed.

This isn't an issue with the old approach because containers hosts
generally do not virtualize those /sys and /proc files.

I suppose it's okay to make this change and maybe add a NEWS entry that
recommends using at least 2 CPUs for containers due to this change.

Thanks,
Florian


  reply	other threads:[~2021-04-27 15:38 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-29 18:25 [PATCH 1/4] Remove architecture specific sched_cpucount optimizations Adhemerval Zanella
2021-03-29 18:25 ` [PATCH 2/4] linux: Use sched_getaffinity for __get_nprocs (BZ #27645) Adhemerval Zanella
2021-04-27 15:38   ` Florian Weimer [this message]
2021-03-29 18:25 ` [PATCH 3/4] linux: Use /sys/devices/system/cpu/possible on __get_nprocs_conf Adhemerval Zanella
2021-05-05 16:53   ` Adhemerval Zanella
2021-05-05 17:54   ` Florian Weimer
2021-05-05 18:06     ` Florian Weimer
2021-05-06 13:03       ` Adhemerval Zanella
2021-05-06 13:51         ` Florian Weimer
2021-05-06 20:07           ` Adhemerval Zanella
2021-05-07 11:07             ` Florian Weimer
2021-05-07 12:43               ` Adhemerval Zanella
2021-05-06 13:17     ` Adhemerval Zanella
2021-03-29 18:25 ` [PATCH 4/4] linux: Remove /proc/cpuinfo fallback on alpha and sparc Adhemerval Zanella
2021-05-05 16:53   ` Adhemerval Zanella
2021-05-05 16:52 ` [PATCH 1/4] Remove architecture specific sched_cpucount optimizations Adhemerval Zanella
2021-05-05 17:28 ` Florian Weimer
2021-05-05 18:25   ` Paul Eggert
2021-05-05 19:52     ` Noah Goldstein
2021-05-06 12:22       ` Adhemerval Zanella
2021-05-06 18:34         ` Noah Goldstein
2021-05-06 13:33     ` Adhemerval Zanella
2021-05-06 13:43       ` Florian Weimer
2021-05-06 16:16         ` Adhemerval Zanella
2021-05-06 16:42           ` Florian Weimer
2021-05-06 16:54             ` Adhemerval Zanella
2021-05-06 17:12       ` Paul Eggert
2021-05-06 17:51         ` Adhemerval Zanella

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87tunrloum.fsf@oldenburg.str.redhat.com \
    --to=fweimer@redhat.com \
    --cc=adhemerval.zanella@linaro.org \
    --cc=crrodriguez@opensuse.org \
    --cc=libc-alpha@sourceware.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).