[GE users] Job time slowed with Hyperthreading ?

pvdmeer pvdmeer at gmail.com
Wed Feb 3 09:12:52 GMT 2010


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Hi,

Even if your question already answered, I'd like to add that hyperthreading is a bit of a disappointment.. With the P4, and also with the current generation of Intel processors. We executed a number of tests, and hyperthreading didn't help. In some cases it even made things worse. Conclusion: limit the amount of slots to the number of physical cores.

With kind regards,

Pieter van der Meer

On Wed, Feb 3, 2010 at 4:06 AM, umanga <aumanga at biggjapan.com<mailto:aumanga at biggjapan.com>> wrote:
Thanks Yann,

That helped me alot!

Regards

jobic wrote:
> umanga wrote:
>> Thanks Daniel,
>>
>> Could you please tell me how I can change the  number of slots this
>> using Qmon ?
>>
>> thanks
> You may use the qconf -mq "partition name" command.
> Then you can change the number of slots.
>
> Yann
>>
>> dagru wrote:
>>> If you use SGE 6.2u5 the correct amount of cores and sockets
>>> per host are reported (see qhost -cb or qstat -F m_core). When you
>>> are using the core binding switch -binding you can let the jobs run
>>> on complete cores (in case of hyperthreading or CMT it will be bound on all
>>> processor numbers representing the selected cores) exclusively.
>>> Isolating jobs from another in this way has also other advantages
>>> like preventing cache pollution and memory access benefits.
>>>
>>> But in any case, how many processes can actually run on the host depends
>>> on your slot configuration and not on the amount of reported CPUs.
>>> You may reduce the amount of slots to 4.
>>>
>>> Cheers
>>>
>>> Daniel
>>>
>>> On 02/02/10 11:12, umanga wrote:
>>>
>>>> Greetings ,
>>>>
>>>> Some of my execution hosts have i7 processors (4 cores with
>>>> HyperThreading ) and SGE show that each of this machine has 8 CPUs.
>>>> I noticed that similar jobs take much more time to finish on these
>>>> processors than on a processors without HT.
>>>> So I disabled HT in CMOS ,but still SGE shows 8 CPUs for this hosts.
>>>> Is there any performance issue with Hyperthreading?
>>>> How can I enable actual physical cores (4) for these hosts?
>>>>
>>>> Thanks in advance.
>>>>
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>>
>
>
> --
> ___________________________
>
> Yann JOBIC
> HPC engineer
> Polytech Marseille DME
> IUSTI-CNRS UMR 6595
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> 5 rue Enrico Fermi
> 13453 Marseille cedex 13
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