[R] More than doubling performance with snow

[Prof Brian Ripley]

On Sun, 23 Nov 2008, Hesen Peng wrote:

> Hey my R buddies,
>
> I installed the "snow" and "rpvm" package on my Lenovo Thinkpad T400
> today. The experiment below gave me a surprise. The time consumed by
> serial processing was several times larger than that taken by parallel
> processing. I'm very curious how this happened. Thank you very much.

Read again!  clusterApply() was not running solve() in this process so you 
do not have the total CPU time, and the elapsed time gain is small.

I would surmise from the times given that you are not using an optimized 
BLAS, which for this problem would make good use of the dual cores.

>
>> library(snow)
>>
>> cc <- makePVMcluster(2)
>>
>> temp <- list(matrix(rnorm(1000000),1000),matrix(rnorm(1000000),1000))
>>
>> system.time(tt <- clusterApply(cc,temp,"solve"))
>   user  system elapsed
>  0.584   0.144   4.355
>> system.time(ttt <- sapply(temp,"solve"))
>   user  system elapsed
>  4.777   0.100   4.901
>
> I'm using Ubuntu 8.10. And here's my CPU info:
>
> processor       : 0
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 23
> model name      : Intel(R) Core(TM)2 Duo CPU     P8400  @ 2.26GHz
> stepping        : 6
> cpu MHz         : 800.000
> cache size      : 3072 KB
> physical id     : 0
> siblings        : 2
> core id         : 0
> cpu cores       : 2
> apicid          : 0
> initial apicid  : 0
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 10
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx
> lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx smx est
> tm2 ssse3 cx16 xtpr sse4_1 lahf_lm
> bogomips        : 4521.96
> clflush size    : 64
> power management:
>
> processor       : 1
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 23
> model name      : Intel(R) Core(TM)2 Duo CPU     P8400  @ 2.26GHz
> stepping        : 6
> cpu MHz         : 800.000
> cache size      : 3072 KB
> physical id     : 0
> siblings        : 2
> core id         : 1
> cpu cores       : 2
> apicid          : 1
> initial apicid  : 1
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 10
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx
> lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx smx est
> tm2 ssse3 cx16 xtpr sse4_1 lahf_lm
> bogomips        : 4521.97
> clflush size    : 64
> power management:
>
> -- 
> 彭河森 Hesen Peng
> http://hesen.peng.googlepages.com/
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595