kernel crash on Intel(R) Xeon(TM) CPU 2.66GHz 4-cpus machine

Jean-Eric Cuendet jec at rptec.ch
Mon Aug 21 14:59:07 UTC 2006


>> OK, one thing left to investigate. Just to be sure, how long have you 
>> run the test? It's about 2h for a single step.
> 
> It took about 30 minutes to perform all tests, then it started it again 
> and I quit it (I thought it was a infinite loop). Should I do it many 
> times?

It's an infinite loop, indeed.
IMO, if you did it 1 time, it's OK.
Though at your place, I would have let it run the whole weekend...

>> It's a HyperThreading processor. It's *seen* as 2 processors / CPU but 
>> in fact it's just useless in the majority of situation. We ended up 
>> disabling it in the BIOS for ours...
> 
> what does it mean exactly? if I disable it, does it mean I lose 
> computational power? 2 processors instead of 4 is of course worst, but 

Yes, 2 are worst than 4. But in HT cases, 2 could be better than 4! :-)

> if two of them are only virtual, then the total power (number of 
> operation per clock tick) should remain similar, am I right?

Not exactly. Hyperthreading is pseudo-processors. In certain cases, you 
get 4 processors. But in the majority of cases, they are useless. In 
fact, you get around 30% more processing power with HT enabled on some 
workloads. And 5% less on others...
If you do certain types of processing with multiple threads, then they 
could help. Disable them at first, then when your freeze is solved, 
re-enable them and bench your app. It could help but it depends on the 
workload.
HT was marketing hype on Intel side IMO.

> Now I disabled HyperThreading, but I could not disable one cpu (at least 
> on the bios setup). Therefore now my kernel has recognized two 
> processors. I've just launched two simulations. Let's see what happens.

OK, to disable the other CPU, run a not-SMP kernel.
Ben? Is there a way to disable one CPU on the kernel command line?
Else, run the i386 kernel (linux-image-386)

Bye.
-jec

-- 
Best regards / Salutations.

Jean-Eric Cuendet
Senior developer / Technical support
Riskpro Technologies SA
Av. Louis-Ruchonnet 2
CH-1003 Lausanne
Switzerland

Direct    : +41 21 637 0123
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