[Beowulf] Re: scalability
Greg at keller.net
Mon Dec 14 07:15:56 PST 2009
On Dec 12, 2009, at 10:41 AM, beowulf-request at beowulf.org wrote:
> From: Gus Correa <gus at ldeo.columbia.edu>
> Hi Amjad
> amjad ali wrote:
>> Hi Gus,
>> I was told that some people used to run two processes only on
>> dual-socket dual-core Xeon nodes , leaving the other two cores
>> Although it is an apparent waste, the argument was that it paid
>> off in terms of overall efficiency.
>> I guess I fully agree with this.
The other reason I see folks choose this is licensing. In some cases
the "cost" of the license tokens to use the extra cores is too
expensive given the minimal benefit since they still compete for
Memory Bandwidth, CPU Cache, or less commonly Network Bandwidth/Latency.
>> But still if it is a shared cluster (as in my case) then the cores
>> left unbusy may be allocated to another process of another user by
>> Batch scheduler. Right??
> Unless you request full nodes, as Chris Samuel suggested:
> #PBS -l nodes=10:ppn=8
> However, beware that this greedy and wasteful behavior
> may drive your system administrator and
> the other cluster users mad at you! :)
> Well, you can always justify it in the name of science, of course. ;)
They may thank you for not sharing a "maxed out" node. If someone is
doing benchmarking or running a similarly sensitive code you're saving
everyone a lot of head scratching. In my world users sharing nodes is
almost always trouble looking for a way to ruin a weekend.
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