How to measure the RAM read/write performance

[Valdis.Kletnieks at vt.edu]

On Wed, 27 Feb 2013 15:38:00 +0530, sandeep kumar said:

> In development phase of the board, we are trying to measure RAM performance
> gain while changing type of the RAM.
> The standard benchmark tools are giving us the Cache performance only. So
> we want to try some method to measure RAM performance.

The fact that you can't measure the effect of RAM speed because the L1/2/3
cache masks the effect should tell you something :)

If you are seeing a 98% hit rate or so, RAM speed will indeed not matter
much.  If you're seeing a poor cache hit ratio, you're most likely to get
better performance not by changing the RAM, but changing the application
to improve its cache usage.

And of course, if the application's design is one that is resistant to
improved cache hit ratios, it is important you measure RAM performance
*with that application running*, not a benchmark.  This is because if your
application is managing to thrash the cache, the resulting RAM access
patterns will be *highly* sensitive to actual program behavior, and any
corner cases in the hardware may or may not be hit by the benchmark the
same way the application does.
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