The Phenom / PhenomII memory controller: ganged vs unganged mode benchmarked

Written by Gionatan Danti on . Posted in Hardware analysis

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Synthetic benchmarks: STREAM

Let's begin our session with a classic memory test: the STREAM benchmark (you can download it at http://www.cs.virginia.edu/stream/). It can be run in single and multi thread mode and, in the latter case, it use the OpenMP library to spread the calculations over the available core. The benchmark was configured to use a 16.000.000 entry array, with each entry using 8 bytes (double precision floating point type). As the test use three arrays, the total memory utilized was about 366 MB (well beyond the 8.5 MB total processor's cache).

STREAM memory benchmark

While in single thread mode the performances of ganged and unganged modes are quite on par, in the multi-threaded scenario the unganged mode score higher. Why? Probably because the use of more threads exacerbate the advantage in writing from and reading to main memory at the same time. The advantage that unganged mode has on single-threaded copy also seems to confirm this point.

Comments   

 
#1 Julián Fernández 2012-07-21 00:40
This was quality reading. Thanks mate.
 
 
#2 Iz 2013-01-24 23:14
Thank you for sharing these insights. I found them most useful indeed.
 
 
#3 asd 2014-03-26 19:17
Your graphs are misleading. You should ALWAYS show the full range in any graph (i.e. starting at 0 value), so the magnitude of the gains can be seen at first glance. This is statistics 101.
At least you labeled your axis.
 
 
#4 Gionatan Danti 2014-03-26 19:29
Quoting asd:
Your graphs are misleading. You should ALWAYS show the full range in any graph (i.e. starting at 0 value), so the magnitude of the gains can be seen at first glance. This is statistics 101.
At least you labeled your axis.


Yes, you are right.

When the differences are small, old OpenOffice Calc versions tend to create graphs which don't start from 0.

I realized that only after the graph were published, and I preferred to leave them unmodified.

Regards.
 
 
#5 Jay 2016-06-06 07:09
Thank you for this in-depth piece. It was the best explanation I've come across, and I've been looking for a while. :)
 
 
#6 SvenBent 2016-08-20 16:11
Ncie read through but really wish the bar graphs wasn;t made so misleading. now i have t ohave a huge focus on et he X-axis to get a indication of how big the diffrent really is.

really bad to not start your graphs at 0
 

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