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

[Gus Correa]

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
>  
>