[mpich-discuss] Why is my quad core slower than cluster

[zach]

Thanks for the info.
I tried all of these things but it does not look like it gave any improvement.
Zach

On Tue, Jul 8, 2008 at 2:52 PM, Gus Correa <gus at ldeo.columbia.edu> wrote:
> PS:
>
> Zach:  A couple of obvious checks, besides Rajeev's important suggestion:
>
> 1) Make sure the SMP kernel is running on your home PC:
> "uname -a"
> (Should show "smp" as part of the string.)
>
> 2) Check if Ubuntu triggers all four cores:
> "cat /proc/cpuinfo". (Should show four "virtual" CPUs.)
>
> Gus Correa
>
> ##########
>
> Rajeev Thakur wrote:
>
> Try using the Nemesis device in MPICH2 if you aren't already. Configure with
> --with-device=ch3:nemesis.
>
> Rajeev
>
>>
>
> Gus Correa wrote:
>
>> Hello  Zach and list
>>
>> From all that I've observed on dual-processor dual-core PCs,
>> and from all that I've read on the web about dual-processor quad-core
>> machines,
>> your results are not alarming, but typical.
>> I was as disappointed as you are, when I saw my speedup results.
>> A lot of people out there had the same frustration too.
>>
>> My benchmarks using a standard climate atmospheric model (NCAR CAM3) on
>> a dual-processor dual-core Xeon workstation showed a speedup factor of 3
>> (not 4),
>> when I moved from one core to four cores.
>> Likewise for a dual-processor dual-core Opteron workstation,
>> I've got a speedup factor slightly below 3.5. (Better than Xeon, but still
>> not 4).
>>
>> The problem seems to get worse with quad-cores, again with the Opterons
>> slightly ahead of the game.
>> Memory/bus contention has been mentioned as the culprit by a lot of
>> people.
>> One core in a multicore doesn't scale as one (single-core) CPU.
>>
>> You will find plenty of references to this problem on the web and on many
>> mailing lists:
>> here in the MPICH list, on the Rocks Cluster list, on the MITgcm list,
>> etc, etc.
>>
>> I hope it heals (as helping it cannot)
>> Gus Correa
>>
> zach wrote:
>
>> I am using a cluster.
>> Each pc has two cpus and they are Xeon. Each cpu has 4GB, i think red
>> hat is running.
>>
>> I also use a pc at home- quad core intel chip, 8gb ram, ubuntu.
>>
>> Both are using mpich.
>>
>> I have found that my home pc is only running about 1/3 the speed of
>> the cluster, and the number of processes (4) and code is the same.
>>
>> Can anyone tell me if this is typical, and why, or am I not optimizing
>> something properly?
>>
>> Thanks
>> Zach
>>
>
>