From: Rich Felker <dalias@libc.org>
To: musl@lists.openwall.com
Subject: Re: __sched_cpucount returns garbage
Date: Tue, 2 Dec 2014 19:11:15 -0500 [thread overview]
Message-ID: <20141203001115.GC4574@brightrain.aerifal.cx> (raw)
In-Reply-To: <20141130113846.GC9258@port70.net>
On Sun, Nov 30, 2014 at 12:38:46PM +0100, Szabolcs Nagy wrote:
> * Isaac Dunham <ibid.ag@gmail.com> [2014-11-29 15:36:33 -0800]:
> > I noticed that nproc ended up on the toybox TODO list (via Tizen), and went
> > poking about via strace and ltrace to see where it got the cpu count from.
> >
> > In the process, I discovered that __sched_cpucount is returning garbage;
>
> works here as expected:
>
> #define _GNU_SOURCE
> #include <sched.h>
> int main()
> {
> cpu_set_t s = {0};
> CPU_SET(3, &s);
> CPU_SET(7, &s);
> CPU_SET(24, &s);
> return __sched_cpucount(sizeof s, &s);
> }
>
> returns 3
>
> > on Alpine Linux on my N270-based netbook (1 physical core but
> > hyperthreading makes it look like 2),
> > nproc
> > outputs a random number of CPUs ranging from 413 to 472.
>
> see where the cpu_set_t argument comes from
> (most likely sched_getaffinity syscall)
> then see why that is broken
>
> __sched_cpucount just counts bit flags
Is it possible that the macros from sched.h are using it wrong, or
that nproc is using __sched_cpucount directly rather than using the
sched.h macros and expecting different behavior from it (perhaps a
mismatch between the musl and glibc behavior, like counting bits vs
bytes vs longs)?
Rich
next prev parent reply other threads:[~2014-12-03 0:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-29 23:36 Isaac Dunham
2014-11-30 11:38 ` Szabolcs Nagy
2014-12-03 0:11 ` Rich Felker [this message]
2014-12-03 1:33 ` Isaac Dunham
2014-12-03 2:48 ` Rich Felker
2014-12-03 3:19 ` Rich Felker
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=20141203001115.GC4574@brightrain.aerifal.cx \
--to=dalias@libc.org \
--cc=musl@lists.openwall.com \
/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).