Re: smp

[Orna Agmon]

Nadav repeated my question at
[EMAIL PROTECTED],
and I got a lot of replies,
so I am summerizing them here, in case anybody else is interested:

On Wed, 1 Aug 2001, Orna Agmon wrote:
> Hi all.
> Last year I was told that linux does not support well an smp of AMD CPU-s,
> only pentium or celeron. Does anybody know if this is (still?) true?
Nadav's question:

Subject: SMP possible with AMD CPUs?

A Linux user in a local Linux club asked me whether Linux support SMP with
AMD (rather than Intel Pentium) CPUs. She said that a year ago she was
told
Linux 2.2 couldn't, and that she was wondering whether the new Linux 2.4
can.
I didn't know the answer, so I started digging.

I tried looking with various search search engines, but found nothing
about
this subject. Looking through the source code, it appears that SMP with
AMDs
*might* be supported, but I couldn't find any comment confirming that. The
relevant FAQs, READMEs, and so on that I found are all from the 2.2 kernel
era.

So, does Linux support SMP on AMD CPUs?

The answers (including Alan Cox's answer):


From: Johannes Erdfelt <[EMAIL PROTECTED]>

Yes. In fact, recent 2.2 kernels (2.2.20 pre patches I believe) and all
2.4 kernels support SMP AMD systems.

(and regarding the faq question):

I don't know if this was true to begin with, but I know that SMP AMD
systems use the APIC SMP scheme Intel defined and uses.

From: Dan Hollis <[EMAIL PROTECTED]>

Yes.

Linux works fine on Tyan Thunder K7 (S2462) with dual AMD athlon.

From: Joel Jaeggli <[EMAIL PROTECTED]>

before the althon amd k6's would have used pic design called the open pic
to do smp... but since nobody implemented the openpic it's kinda hard to
use it...

the combination of the athlon mp and the amd 761 chipset will do
multiprocessor support without trouble... you will want to use 2.4 becuase
lots of devices on the boards  aren't supported by 2.2...

From: "Bill Rugolsky Jr." <[EMAIL PROTECTED]>

Does this answer your question? :-)

[rugolsky@k7 rugolsky]$ uname -a
Linux k7 2.4.6-2.4smp #1 SMP Sat Jul 21 17:28:23 EDT 2001 i686 unknown

[rugolsky@k7 rugolsky]$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 6
model name      : AMD Athlon(tm) Processor
stepping        : 1
cpu MHz         : 1194.684
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
cmov
pat pse36 mmx fxsr syscall mmxext 3dnowext 3dnow
bogomips        : 2385.51

From: Mark Hahn <[EMAIL PROTECTED]>

it does.  apics are intel-compatible.

****************************************************************
From: Alan Cox <[EMAIL PROTECTED]>
To: Joel Jaeggli <[EMAIL PROTECTED]>
Cc: Nadav Har'El <[EMAIL PROTECTED]>, [EMAIL PROTECTED],
     [EMAIL PROTECTED]
Subject: Re: SMP possible with AMD CPUs?

> the combination of the athlon mp and the amd 761 chipset will do
> multiprocessor support without trouble... you will want to use 2.4
becuase
> lots of devices on the boards  aren't supported by 2.2...

Athlon SMP will actually not always work with 2.2. Quite a few folks
reported problems and patches for 2.2.20pre fixes that and broke other
stuff so got reverted.

2.4 seems to do the job nicely
*******************************************************************


From: Luigi Genoni <[EMAIL PROTECTED]>
Runs stable and fast on a dual Athlon 1.2 Ghz, amd chipset.
tested with kernel 2.4.6 and 2.4.7

From: Stephen Torri <[EMAIL PROTECTED]>
To: Alan Cox <[EMAIL PROTECTED]>
Cc: Joel Jaeggli <[EMAIL PROTECTED]>,
     Nadav Har'El <[EMAIL PROTECTED]>, [EMAIL PROTECTED],
     [EMAIL PROTECTED]
Subject: Re: SMP possible with AMD CPUs?

Are the AMD CPUs really geared at the silicon level for true SMP? Some
friend of mine says that just because you can pull the state pin by a
chipset to remove the CPU and start another doesn't say the CPU is really
made for SMP. It just says that they have made it work through the
chipset. I am not sure if the Intel family are really true SMP or not.

I would apprecite some feedback on this.

Stephen

From: Johannes Erdfelt <[EMAIL PROTECTED]>
To: Alan Cox <[EMAIL PROTECTED]>

> Athlon SMP will actually not always work with 2.2. Quite a few folks
> reported problems and patches for 2.2.20pre fixes that and broke other
> stuff so got reverted.
>
> 2.4 seems to do the job nicely

I sent you a new patch which fixes the problem.

Here's the original with the new patch as well.

JE

From: [EMAIL PROTECTED]

Hmmm.. I seem to recall Tyan once built a board that did OpenPIC, and I
think Fry's (funky computer/consumer electronics store in Western US)
carried it for a month or two. Just rumour?

From: Vivek <[EMAIL PROTECTED]>

We just had an SMP Athlon box delivered to work today - It's got either RH
or Debian on it [most of our x86 unix boxes are debian, but there a few
people who seem to like RH more. Go figure :)]. There's only one SMP/AMD
motherboard, and I think it's only come out recently - not sure how stable
everything is, it's still in shakedown - there are a couple of quibbles
that might be kernel related, or might be hardware related. But basically,
the anser is yes, but don't use it for anything critical until the
platform's been pounded on for a while longer.