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-   -   kernel processor family influence ? (http://www.linuxquestions.org/questions/linux-kernel-70/kernel-processor-family-influence-689262/)

ofpeled 12-09-2008 04:02 AM

kernel processor family influence ?
 
Hey,
Can please you explain to me what and where is the effect (if there is one ) on choosing a core2/Xeon processor family instead of P4?

Is this relevant to 32bit systems ?
will i get better memory management?

thanks.

pinniped 12-09-2008 09:03 PM

The Xeon series is the high-end pentium originally intended for low-end servers. Memory management will not improve; that is up to the kernel, not so much the CPU. If you want to run these machines in 32-bit mode (or 64) that is up to you.

Look at a comparison of the Xeon and P4 chips you are interested in; the usual difference between the cheaper desktop CPUs and the Xeon are in cache size and cache levels. There are probably other differences as well such as an interconnect bus for N-way CPUs. If you don't understand what all the differences are, you probably don't need the more expensive option.

stress_junkie 12-09-2008 09:03 PM

I've built a couple of desktop computers using the core 2 desktop CPUs. I don't see much difference in performance on the desktop if the P4 is the same clock rate as the core 2. On the other hand my E8400 really does a great job running the Folding at Home client software. The 6MB of shared L2 memory on the CPU probably keeps the FAH client software in the cache all the time. I'm finishing work units like crazy and I configured it to get the big jobs. I've finished 11 work units since November 30th. Compared that with my two AMD Athlon XP computers that take 60 hours per work unit.

The one really nice thing about the core 2 CPUs is that they only consume 65 watts of electricity compared to 95-150+ watts for P4s.

I expect that the Xeon line would be similar.

ofpeled 12-10-2008 12:26 AM

Ok my bad i wasn't clear :) .
I know very well the differences between cpu types in performance.
My question is: when i'm compiling a kernel on a new Xeon server. what will it matter if i compile it picking the new Core2/Xeon processor family or the Pentium 4/ older xeon processor family ( all are 8586 compatible).
and to that matter Amd processor too, i already tried running a kernel compiled with the processor type option in the kernel config = P4.
and it worked fine on new Quad core servers, cat /proc/cpuinfo showed all the cores since another option in the kernel config was picked - support multiple cores.

Does this option in the kernel .config (processor family)has any effect? and if so, on what ?

pinniped 12-10-2008 01:33 AM

Ah, OK. You *should* select the correct family of CPU because there may be differences in the instruction sets; choosing the correct family also ensures that the kernel makes the best use of available features (if a kernel programmer considers the feature worth the effort of adding CPU-specific code). So the worst case in choosing the wrong family is that the CPU generates a software trap when it encounters an unknown instruction; the best case is that the CPU runs fine but the kernel does not make use of some extra features; in some cases this could mean a significant difference in performance - as an extreme example, consider the 80286 vs Pentium - the 80286 did not have an FPU included in the CPU package.

ofpeled 12-10-2008 01:41 AM

Thanks for the quick reply - pinniped
Can you point on suck differences between P4 family and new Core2 family and AMD, that the kernel programmers did include in the kernel package? or where can i find info about this? i need real evidence.


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