[uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[Stanislav Meduna]

Hi,

the following program

===
#include <unistd.h>
#include <stdio.h>

main()
{
   printf("Number of processors: %d\n", sysconf(_SC_NPROCESSORS_CONF));
}
===

produces

   Number of processors: 0

on my system.


# uname -a
Linux dirk 2.6.26 #1 Wed Jul 30 10:56:10 CEST 2008 i686 GNU/Linux

# cat /proc/cpuinfo
processor       : 0
vendor_id       : User Mode Linux
model name      : UML
mode            : skas
host            : Linux seldon-base 2.6.23.17 #2 SMP Sat Jun 21 15:04:22 CEST 2008 i686
bogomips        : 4771.02

# ls -l /lib/libc.so.6
lrwxrwxrwx 1 root root 11 2008-07-17 17:16 /lib/libc.so.6 -> libc-2.7.so


The monit monitoring tool (http://www.tildeslash.com/monit/)
crashes because of this. I don't know whose fault it is, but
I suspect the UML - otherwise I'd expect many more instances
of this problem when googling for it.


Regards
-- 
                                 Stano

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Re: [uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[Jeff Dike]

On Mon, Aug 04, 2008 at 03:58:04PM +0200, Stanislav Meduna wrote:
> Hi,
> 
> the following program
> 
> ===
> #include <unistd.h>
> #include <stdio.h>
> 
> main()
> {
>    printf("Number of processors: %d\n", sysconf(_SC_NPROCESSORS_CONF));
> }
> ===
> 
> produces
> 
>    Number of processors: 0
> 
> on my system.

Works here...

[root@uml-test ~]# cc -o ncpus ncpus.c 
[root@uml-test ~]# ./ncpus 
Number of processors: 1

sysconf seems to be looking at /proc/stat, which looks like this here:

	cpu  80 0 157 12771 984 0 0 0 0
	cpu0 80 0 157 12771 984 0 0 0 0
	intr 15259 12519 0 75 0 2590 0 0 0 0 0 0 74 0 0 1
	ctxt 8081
	btime 1217881784
	processes 1144
	procs_running 3
	procs_blocked 0

I'd guess it's looking at the cpu0 (and cpu<n>) lines.

    	       	       	  Jeff

-- 
Work email - jdike at linux dot intel dot com

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Re: [uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[Stanislav Meduna]

Jeff Dike wrote:

> sysconf seems to be looking at /proc/stat, which looks like this here:
> 
> 	cpu  80 0 157 12771 984 0 0 0 0
> 	cpu0 80 0 157 12771 984 0 0 0 0
> 	intr 15259 12519 0 75 0 2590 0 0 0 0 0 0 74 0 0 1
> 	ctxt 8081
> 	btime 1217881784
> 	processes 1144
> 	procs_running 3
> 	procs_blocked 0
> 
> I'd guess it's looking at the cpu0 (and cpu<n>) lines.

# cat /proc/stat
cpu  38822 537 3376 46871329 174924 0 9 0 0
cpu0 38822 537 3376 46871329 174924 0 9 0 0
intr 47644940 47088997 0 5 0 395871 160067 0 0 0 0 0 0 0 0 0
ctxt 9822902
btime 1217412992
processes 26529
procs_running 2
procs_blocked 0


Hmmm... so I have cpu0 similar to yours. What version
of UML and libc do you have?

-- 
                                   Stano

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Re: [uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[Jeff Dike]

On Mon, Aug 04, 2008 at 10:59:36PM +0200, Stanislav Meduna wrote:
> Hmmm... so I have cpu0 similar to yours. What version
> of UML and libc do you have?

UML 2.6.26 and an older libc:

% ls -l /lib/libc.so.6
lrwxrwxrwx 1 root root 11 Jun  2  2007 /lib/libc.so.6 -> libc-2.5.so

Looking through libc at

http://www.google.com/codesearch?hl=en&q=file:\.c%24+\"/stat\"+package:http://su-se.lunar-linux.org/lunar/mirrors/glibc-2.3.3-cvs-20040708.tar.bz2+show:m1O9RV1wlw4:qbkros5194A:MbxD3_8dUHU&sa=N&cd=1&ct=rc&cs_p=http://su-se.lunar-linux.org/lunar/mirrors/glibc-2.3.3-cvs-20040708.tar.bz2&cs_f=glibc-2.3.3-cvs-20040708/sysdeps/unix/sysv/linux/getsysstats.c

I see it counting cpu<n> lines in /proc/stat, which is what I'm
seeing.  It will also look at /proc/cpuinfo.  Can you strace your
version and see if it's looking there at all?

	     	       	  Jeff


-- 
Work email - jdike at linux dot intel dot com

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Re: [uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[Stanislav Meduna]

Jeff Dike wrote:

> I see it counting cpu<n> lines in /proc/stat, which is what I'm
> seeing.  It will also look at /proc/cpuinfo.  Can you strace your
> version and see if it's looking there at all?

No.. looks like they changed the method:

open("/sys/devices/system/cpu", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|0x80
000) = 3
fstat64(3, {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
fcntl64(3, F_GETFD)                     = 0x1 (flags FD_CLOEXEC)
getdents64(3, /* 5 entries */, 4096)    = 144
getdents64(3, /* 0 entries */, 4096)    = 0
close(3)                                = 0

No reference to /proc/stat nor /proc/cpuinfo.

# ls -l /sys/devices/system/cpu
-r--r--r-- 1 root root 4096 2008-08-04 23:51 online
-r--r--r-- 1 root root 4096 2008-08-04 23:51 possible
-r--r--r-- 1 root root 4096 2008-08-04 23:51 present

# cat /sys/devices/system/cpu/online
0
# cat /sys/devices/system/cpu/possible
0
# cat /sys/devices/system/cpu/present
0


On another Linux (real, 2.6.18) this looks completely
different:

$ ls -l /sys/devices/system/cpu
total 0
drwxr-xr-x 4 root root 0 2008-08-04 23:53 cpu0


$ ls -l /sys/devices/system/cpu/cpu0/
total 0
drwxr-xr-x 5 root root    0 2007-06-11 09:30 cache
-r-------- 1 root root 4096 2008-08-04 23:53 crash_notes
drwxr-xr-x 2 root root    0 2007-06-11 09:30 topology


Well.. so this is an interface definition problem.. now who has
changet something and did not tell the others..


-- 
                                   Stano

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Re: [uml-devel] sysconf(_SC_NPROCESSORS_CONF) returning zero

[Ingo van Lil]

Jeff Dike schrieb:

>> Hmmm... so I have cpu0 similar to yours. What version
>> of UML and libc do you have?
> 
> UML 2.6.26 and an older libc:
> 
> % ls -l /lib/libc.so.6
> lrwxrwxrwx 1 root root 11 Jun  2  2007 /lib/libc.so.6 -> libc-2.5.so
> 
> Looking through libc at
> 
> http://www.google.com/codesearch?hl=en&q=file:\.c%24+\"/stat\"+package:http://su-se.lunar-linux.org/lunar/mirrors/glibc-2.3.3-cvs-20040708.tar.bz2+show:m1O9RV1wlw4:qbkros5194A:MbxD3_8dUHU&sa=N&cd=1&ct=rc&cs_p=http://su-se.lunar-linux.org/lunar/mirrors/glibc-2.3.3-cvs-20040708.tar.bz2&cs_f=glibc-2.3.3-cvs-20040708/sysdeps/unix/sysv/linux/getsysstats.c
> 
> I see it counting cpu<n> lines in /proc/stat, which is what I'm
> seeing.  It will also look at /proc/cpuinfo.  Can you strace your
> version and see if it's looking there at all?

More recent versions of glibc (here: 2.8 on Fedora 9) seem to look at 
the contents of /sys/devices/system/cpu instead. That directory is empty 
in UML, which might explain the odd result from Stanislav's program.

Cheers,
Ingo

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