From: Szabolcs Nagy <nsz@port70.net>
To: musl@lists.openwall.com
Cc: Michael Jeanson <mjeanson@efficios.com>,
Richard Purdie <richard.purdie@linuxfoundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Jonathan Rajotte-Julien <jonathan.rajotte-julien@efficios.com>
Subject: Re: sysconf(_SC_NPROCESSORS_CONF) returns the wrong value
Date: Tue, 26 Mar 2019 18:45:41 +0100 [thread overview]
Message-ID: <20190326174540.GH26605@port70.net> (raw)
In-Reply-To: <20190326162334.GF17481@joraj-alpa>
* Jonathan Rajotte-Julien <jonathan.rajotte-julien@efficios.com> [2019-03-26 12:23:34 -0400]:
> > i think we need to know why does a process care if musl returns
> > the wrong number? or what are the valid uses of such a number?
> > (there are heterogeous systems like arm big-little, numa systems
> > with many sockets, containers, virtualization,.. how deep may a
> > user process need to go down in this rabbit hole?)
>
> Does the answers from Mathieu Desnoyers [1] and Florian Weimer [2] fit the bill?
yes
>
> [1] https://www.openwall.com/lists/musl/2019/03/16/3
> [2] https://www.openwall.com/lists/musl/2019/03/19/1
> >
> > note that most of /sys/devices/system/cpu/* is documented under
> > Documentation/ABI/testing in linux, not in Documentation/ABI/stable
> > and the format is not detailed, and some apis (e.g. /proc/cpuinfo)
> > are known to be different on android (and grsec?) kernels it may
> > be unmounted during early boot or in chroots, so sysfs parsing is
> > only done when really necessary.
>
> For what it's worth, uclibc and uclibc-ng seem to iterate over
> /sys/devices/system/cpu/* and fallback on online calculation if necessary.
>
> https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/unistd/sysconf.c#n102
>
> In the mean time, we implemented a fallback similar to this when we do not "know"
> the libc used (since musl does not come with __musl__, I read the reasons why,
> no need to discuss this).
>
> Not sure of the direction musl should take but I strongly believe that the
> behaviour regarding _SC_NPROCESSORS_CONF is not the appropriate one.
i agree that the current behaviour is not ideal, but
iterating over /sys/devices/system/cpu/cpu* may not
be correct either.. based on current linux api docs.
i don't understand why is that number different from the
cpu set in /sys/devices/system/cpu/possible
it seems any upper bound on the number of cpus would be
valid but it's not clear how to provide that guarantee.
next prev parent reply other threads:[~2019-03-26 17:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-15 21:02 Jonathan Rajotte-Julien
2019-03-16 2:25 ` Szabolcs Nagy
2019-03-16 13:58 ` Mathieu Desnoyers
2019-03-16 14:28 ` Jonathan Rajotte-Julien
2019-03-19 19:11 ` Florian Weimer
2019-03-26 16:23 ` Jonathan Rajotte-Julien
2019-03-26 17:45 ` Szabolcs Nagy [this message]
2019-03-26 18:01 ` Mathieu Desnoyers
2019-04-02 19:02 ` Szabolcs Nagy
2019-04-02 22:38 ` Mathieu Desnoyers
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=20190326174540.GH26605@port70.net \
--to=nsz@port70.net \
--cc=jonathan.rajotte-julien@efficios.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mjeanson@efficios.com \
--cc=musl@lists.openwall.com \
--cc=richard.purdie@linuxfoundation.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.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
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 NNTP newsgroup(s).