Re: Detecting SMP

Re: Detecting SMP

[Jay D Allen]

What is the platform ( x86, Sparc, alpha or ?)?  On sparc look in the
bootprom (ls /proc/openprom) that works regardless of kernel SMP status.
On Intel I think your out of luck, at least with the commonly available
hardware/software.  In theory there could be a bios-peeking structure in
/proc much like openprom that could give you hints...



Sent by:  linux-kernel-owner@vger.kernel.org

To:   linux-kernel@vger.kernel.org
cc:
Subject:  Detecting SMP



Hello. Is there a way, when running a non-SMP kernel, to detect or
otherwise tell (software only; the machine is 2400 miles away) if the
system has SMP capibilties? Would /proc/cpuinfo show two CPUs if the
kernel is non-SMP?  Thanks!

(btw, the kernel in question is a stock RH6.2 kernel 2.2.14-5, and yes, I
know I should update it anyways and that a SMP kernel will run on a UP
system)

--
Burton Windle                 burton@fint.org
Linux: the "grim reaper of innocent orphaned children."
          from /usr/src/linux-2.4.0/init/main.c:655

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Detecting SMP

[Burton Windle]

Hello. Is there a way, when running a non-SMP kernel, to detect or
otherwise tell (software only; the machine is 2400 miles away) if the
system has SMP capibilties? Would /proc/cpuinfo show two CPUs if the
kernel is non-SMP?  Thanks!

(btw, the kernel in question is a stock RH6.2 kernel 2.2.14-5, and yes, I 
know I should update it anyways and that a SMP kernel will run on a UP
system)

-- 
Burton Windle				burton@fint.org
Linux: the "grim reaper of innocent orphaned children."
          from /usr/src/linux-2.4.0/init/main.c:655

Re: Detecting SMP

[Tigran Aivazian]

yes, just run the famous mptable program. If the machine is SMP then it
will have a valid Intel MP 1.4 configuration tables so the program will
show meaningful output.

Regards,
Tigran

On Tue, 20 Feb 2001, Burton Windle wrote:

> Hello. Is there a way, when running a non-SMP kernel, to detect or
> otherwise tell (software only; the machine is 2400 miles away) if the
> system has SMP capibilties? Would /proc/cpuinfo show two CPUs if the
> kernel is non-SMP?  Thanks!
> 
> (btw, the kernel in question is a stock RH6.2 kernel 2.2.14-5, and yes, I 
> know I should update it anyways and that a SMP kernel will run on a UP
> system)
> 
> 

Re: Detecting SMP

[Jeff Garzik]

On Wed, 21 Feb 2001, Tigran Aivazian wrote:
> yes, just run the famous mptable program. If the machine is SMP then it
> will have a valid Intel MP 1.4 configuration tables so the program will
> show meaningful output.

Does that allow you to detect multiple processors... or just an SMP board?

	Jeff

Re: Detecting SMP

[Tigran Aivazian]

On Wed, 21 Feb 2001, Jeff Garzik wrote:

> On Wed, 21 Feb 2001, Tigran Aivazian wrote:
> > yes, just run the famous mptable program. If the machine is SMP then it
> > will have a valid Intel MP 1.4 configuration tables so the program will
> > show meaningful output.
> 
> Does that allow you to detect multiple processors... or just an SMP board?
> 

the answer is in section 4.1 of the Intel MP 1.4 spec:

   "An MP-compliant system must implement the MP floating pointer
    structure, ..."

So, one would normally expect this to mean an SMP board rather than
multiple processors, _HOWEVER_, I can imagine a very clever MP-aware BIOS
implementation which detects that there are many processors and prepares
MP floating config table and does _not_ prepare it otherwise. So, it all
depends on the BIOS implementation.

Actually, I never tried unplugging all-1 processors from my SMP machines
and seeing what sort of MP table is left...

Regards,
Tigran

Re: Detecting SMP

[Maciej W. Rozycki]

On Wed, 21 Feb 2001, Tigran Aivazian wrote:

> So, one would normally expect this to mean an SMP board rather than
> multiple processors, _HOWEVER_, I can imagine a very clever MP-aware BIOS
> implementation which detects that there are many processors and prepares
> MP floating config table and does _not_ prepare it otherwise. So, it all
> depends on the BIOS implementation.

 I've seen systems that do so and while it's not forbidden I consider it a
bad thing.  It prevents us from being able to use I/O APICs.

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +

Re: Detecting SMP

[Tigran Aivazian]

On Wed, 21 Feb 2001, Tigran Aivazian wrote:

> yes, just run the famous mptable program.

before I am snowed under with questions about where to get this program,
here is the src and binaries that I use -- it is quite possible that there
is a newer version (I suspect Ingo Molnar might know better :)

http://www.moses.uklinux.net/mptable

Regards,
Tigran

Re: Detecting SMP

[Mike A. Harris]

On Tue, 20 Feb 2001, Burton Windle wrote:

>Hello. Is there a way, when running a non-SMP kernel, to detect or
>otherwise tell (software only; the machine is 2400 miles away) if the
>system has SMP capibilties? Would /proc/cpuinfo show two CPUs if the
>kernel is non-SMP?  Thanks!
>
>(btw, the kernel in question is a stock RH6.2 kernel 2.2.14-5, and yes, I
>know I should update it anyways and that a SMP kernel will run on a UP
>system)

Yes, there are several ways.  How do you want to know how to do
it, in C, or a bash script?  sysconf is one way, parsing
/proc/cpuinfo and /proc/stat is another.  Beware though, if you
parse /proc/cpuinfo or stat, it is very different on different
architectures, particularly sparc.

Here is some code which should do it more or less correctly on
any arch:

ncpus=$(egrep -c ^cpu[0-9]+ /proc/stat || :)
[ "$ncpus" = "0" ] && ncpus=1


----------------------------------------------------------------------
    Mike A. Harris  -  Linux advocate  -  Free Software advocate
          This message is copyright 2001, all rights reserved.
  Views expressed are my own, not necessarily shared by my employer.
----------------------------------------------------------------------
if (argc > 1 && strcmp(argv[1], "-advice") == 0) {
    printf("Don't Panic!\n");
    exit(42);
}