Activating a proc under RedHat 3 AS..and more

[Paprocki]

Hi all, i need your help on this :

I had installed a 8 nodes cluster with Oscar 4.0
My servers are DL140 Proliant. The OS: RedHat 3 AS (kernel 2.4-21)
The installation was made with the hyperthreading enabled in the BIOS.
When i look /proc/cpuinfo i see then 4 procs, all is "normal"

The problem is that when i desactive the hyperthreading in the BIOS, the OS see 2 procs but it use one physical proc only(same physical id in /proc/cpuinfo), the other is desactivated ; it's desactivated 'cause when i type dmesg i see :
"enabling the CPU according to the ACPI table..." I don't know what it means..and later i see that on proc is divided and the other is desactivated...
In my kernel, hyperthreading is desactivated...

So the perf are poor, and it's for a calcul cluster!! ;-(

My question is: someone can explain this comportment to me?And how do i do to have my TWO physical procs activated.???

Thanks!!!!

[xyko_1]

Hi Paprocki,

if ht is enable all cpus becames operational and you have good performance ?

If you have the same behavior with and without ht you may be running a non-smp kernel. verify it.

regards,
xyko

[Paprocki]

the perf are not very good in an hyperthreading environnement..

If i run q non-smp kernel, i won't use my bipro anymore no..?

[xyko_1]

A non-smk kernel is not prepared to dispatch work to more then one cpu, so youn will have poor performance.

On Linux you may have kernels suited to one or more cpus and prepared to work with big rams or not. To have all your hardware been used you have to use the right kernel configuration.

On AS 2.1 that I'm running I may find on /usr/src/linux/configs, configuration files to rebuild you kernel with the basic of your needs, and you may customize it with your personal needs. I guess that 3.0 has the same structure.

regards,
xyko

[Stuart Browne]

To run in multi-processor mode (regardless of hyperthreading), you have to be running an SMP kernel.

There are multiple options in the BIOS about processors. There's Hyperthreading, as well as multi-processor modes. Ensure that you've not disabled the wrong one.

All that being said, I wouldn't expect the enabled Hyperthreading to cause any issues whats-so-ever. At worst, you'll get no performance boost.