[Beowulf] Thought that this might be of interest

Joe Landman landman at scalableinformatics.com
Mon Nov 6 11:04:00 EST 2006


Richard Walsh wrote:
> Joe Landman wrote:
>> We are working on a machine with 2 Opteron 2218s.  For laughs, I ran 
>> streams on it.  Here are 1,2,3,4 processor data.
>>
>> 1 processor:
>>
>> Copy:       5713.9944      0.0591      0.0560      0.0600
>> Scale:      5713.9822      0.0587      0.0560      0.0600
>> Add:        5454.2389      0.0911      0.0880      0.0920
>> Triad:      5454.1576      0.0916      0.0880      0.0920
>>
>     Mmmm ... these actually seem low considering the bus bandwidth is 
> supposed to be 10.67 GB/sec

Heh.... don't shoot the measurer ... :)

I agree BTW that I expected this to be about 7++ GB/s per socket.  This 
is a pathscale built binary.  Will try with PGI and Intel as well.

>     in the socket F.  Using the 75% rule (1 silent read, 2 actual reads, 
> and 1 write) from the triad shouldn't
>     we get:
> 
>     10.67 * .75 =  ~8 GBs/sec

Possibly...  The bandwidth per socket is 10.67 GB/s.  So the two thread 
on one socket should be pretty darned close to that.  I am surprised 
that it wasn't.

  Moreover, other folks seem to note what we observed: 
http://tweakers.net/reviews/646/5 with about 5.3 GB/s BW/core.  I think 
affinity is keeping two threads on the same core, so it might take a 
little bit of work to get a real 1 thread/socket number.

[...]

>> 4 processors:
>> Copy:      13332.7765      0.0302      0.0240      0.0360
>> Scale:     13332.7765      0.0262      0.0240      0.0320
>> Add:       13332.6220      0.0400      0.0360      0.0480
>> Triad:     14999.0756      0.0391      0.0320      0.0480
>     These are the numbers I would expect here  ... about 70% of  2 * 
> 10.67 GBs/sec.
>     I think that your out-"liar" is actually giving you the correct 
> numbers.

Possible.  I was expecting something north of 12 GB/s.




-- 

Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: landman at scalableinformatics.com
web  : http://www.scalableinformatics.com
phone: +1 734 786 8423
fax  : +1 734 786 8452 or +1 866 888 3112
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