CPU cache size /proc/cpuinfo is wrong?

omg-ffs · 10-01-2004, 08:59 AM

Lo all,

My CPU cache size appears to be displaying wrong, when I do a cat /proc/cpuinfo I get:

Code:

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Intel(R) Xeon(TM) CPU 3.06GHz
stepping        : 5
cpu MHz         : 3067.505
cache size      : 512 KB
-edit-

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Intel(R) Xeon(TM) CPU 3.06GHz
stepping        : 5
cpu MHz         : 3067.505
cache size      : 512 KB
-edit-

The cpu cache size should be reported as 1Mb and not 512KB. The processors were recently upgraded, doing a cat /proc/cpuinfo under the old cpu;s would of given me a list of 4 cpu's. Yet here, same system (other than the 2 new cpu's) And it is only showing 2 cpu's, rather than the (what I was expecting) virtual extra 2 cpu's. So why the difference?

How can I verfiy the correct cache size on the cpu's? (anything in bios isnt an option as the comp is remotely located).

Can any CPU guru shed some light on this?

Thanks

Electro · 10-01-2004, 02:30 PM

If you enabled hyperthreading, it takes half your cache to make two virtual processors. It seems that someone just took out all the processors and placed one processor. Try seeing if top shows four processors. If it does not and you have compiled your kernel with SMP support, you will have to complain.

omg-ffs · 10-01-2004, 06:13 PM

Hi Electro,

top only shows 2 cpu's:

Code:

Tasks:  99 total,   1 running,  97 sleeping,   0 stopped,   1 zombie
 Cpu0 :  8.3% us,  3.7% sy,  0.0% ni, 86.7% id,  0.0% wa,  0.3% hi,  1.0% si
 Cpu1 : 27.6% us,  1.7% sy,  0.0% ni, 70.4% id,  0.0% wa,  0.0% hi,  0.3% si

I originally had 2x 2.4GHz 512kb cache cpu's, when I did a cat /proc/cpuinfo it would return 4 'individual' cpu's. I then upgraded to 2x 3.06GHz 1Mb cache cpu's and now as I mention - I only get 2 cpu's listed from /proc/cpuinfo, with top only showing two aswell - with the cache size apparently wrong.

My flavour of kernel is 2.6.5-1.358smp Fedora Core 2. The latest stable is 2.6.8.1 - so I'm not exactly on an old kernel.

If /proc/cpuinfo is a hook into the kernel, and that is showing only 2 cpu's, then I assume any program will show only 2 cpu's even if it should be showing 4? So how can I verify for 100% sure the specifications of the cpu's? I have googled this a fair bit and it is not unknown for some cpu's to have the wrong cache size / name shown etc.

Is there another way to check the cpu specs? Or will I have to do a custom kernel build? Don't see why this would be needed, as top etc was showing 4cpu's before the upgrade so it must have SMP support enabled...

Any more ideas?

J.W. · 10-01-2004, 07:35 PM

I don't know if I can help or not, but I'd ask a couple of very basic questions first.

1. Did you open up the box, and can you physically see that there are in fact 2 CPU's installed? If so, are they properly connected, powered, cooled, etc?
2. If so, have you tried manually removing them, then reseating them into their sockets just to be sure it's not a poor connection problem?
3. Are you using the same kernel as you were when you saw the 4 CPU's, or are you using a different version? If it's a different version, can you reboot using the old kernel, and if so, do the 4 CPU's now appear?

To be honest with you, it seems like the most likely explanation for what you're seeing is either:

* you only actually have one CPU installed in the system
* one CPU is functional but the other one is defective in some way
* you need to enable SMP

Good luck with it, either way -- J.W.

omg-ffs · 10-02-2004, 01:28 PM

hi JW,

The box is colocated, so there is no way for me to check the number of cpu's etc, so I can't try out your nos. 2 idea either... The kernel however is exactly the same, everything hardware & software wise (except for the new cpu's) Is the same both before and after the upgrade.

Perhaps a setting in BIOS has defaulted to off or something with the new CPU install? If so which setting could potentially of caused this?

Surely there has to be a way to verify the cpu number & configuration just over SSH though? I'll email supermicro & intel and see if they can advise anything, though if you have more ideas

Thanks.

Electro · 10-02-2004, 04:25 PM

Like I said complain or tell someone at the remote place to stick their head in the computer and found out if there is two processors. Asking Supermicro and Intel will suggest something if the people at the remote area has done everything they could physically to fix the problem.

J.W. · 10-02-2004, 05:38 PM

I agree with Electro - somebody trustworthy needs to open the box and take a look at what's installed. CPU detection should be automatic, just like with the RAM. (Meaning that it's not like you have to get into BIOS and make changes to it if you happen to throw another stick of RAM in there - it's detected automatically.)

I'll admit that I am definitely *not* the expert on multiple CPU systems, so any of my comments should be discounted appropriately, however, if you were able to see 4 virtual CPU's under the old kernel and now you only see two, and the only change was that the old CPU's were removed and new equipment was added, then I'd seriously question that new equipment. If you're only seeing one CPU, then most likely there is only one CPU present in your machine. There's no way to determine that though without someone physically inspecting it.

Good luck with it either way, but I'm beginning to think that your order might have been screwed up, and instead of shipping 2 Xeon's, only one was sent/installed, or maybe one is defective. Like I said though I'm far from the expert, so anyone with better knowledge and experience, please chime in. -- J.W.

omg-ffs · 10-03-2004, 05:16 PM

Thanks for the words guys.

J.W. · 10-03-2004, 09:04 PM

Well good luck with it omg-ffs. To be honest I'd be curious as to how this turns out. If you'd be willing to post back a follow-up, I can say for sure that I'd be interested in seeing it, and my bet would be that Electro and anyone else reading this thread would be too. Whatever the outcome I hope in the end it works out favorably for you -- J.W.

Caissa · 10-13-2004, 11:46 AM

I would suggest rebooting the nodes and checking what it says on bootup, rather than relying on /proc/cpuinfo.

When I boot up an older Dell PowerEdge1750 with 512K cache, it says on bootup:

Two Xeon CPUs, 2.4GHz L2 Cache: 512 KB

When I boot up a newer Dell PowerEdge1750 with 1 MB cache, it says on bootup:

Two Xeon CPUs, 3.06GHz L2 Cache: 512 KB L3 Cache: 1MB

/proc/cpuinfo reports on both of these machines 4 CPUs (because of hyperthreading enabled), each with 512 K cache.

I think that /proc/cpuinfo, based on this, notes only the L2 cache, which happens to be the same on both of these machines.