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Date: Tue, 2 Dec 2014 19:11:15 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: __sched_cpucount returns garbage
On Sun, Nov 30, 2014 at 12:38:46PM +0100, Szabolcs Nagy wrote:
> * Isaac Dunham <ibid.ag@...il.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
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