CODEWITHSUNDEEP
c#c++chardwareperformancecounter
Tom De Bie
Tom De Bie

Reputation: 93

Memory Bandwidth Usage

How do you calculate memory (RAM) bandwidth used? Which performance counters are required?

I came across a tool that was able to do it, the "Rightmark multi-threaded memory test". But unlike the rest of Rightmark's tests, I haven't found the source code for it, just the binaries

Upvotes: 5

Views: 1651

Answers (2)

user9876
user9876

Reputation: 11102

If your code can run on Linux, use Cachegrind:

Cachegrind is a cache profiler. It performs detailed simulation of the I1, D1 and L2 caches in your CPU and so can accurately pinpoint the sources of cache misses in your code. It identifies the number of cache misses, memory references and instructions executed for each line of source code, with per-function, per-module and whole-program summaries. It is useful with programs written in any language. Cachegrind runs programs about 20--100x slower than normal.

You may want to use the KCacheGrind GUI.

Upvotes: 2

sybreon
sybreon

Reputation: 3156

It is very difficult to 'calculate' memory bandwidth usage. There are lots of non-trivial cache and MMU issues to contend with. The only real way to do it is either through the use of simulation or real-world measurements.

You can get a 'rough' idea by debugging the code and counting the number of memory load and store operations performed. However, knowing whether it was a cache hit/miss is another issue.

It depends on your purpose. If it is to obtain a guesstimate, you can use the rule of thumb that about 30% of general purpose code is memory loads and stores. If you're trying to get a worst case, you can assume that caches miss all the time and work it out.

One potential thing you could do is to look at virtualisation. There are several open source options (QEMU comes to mind). It may be possible to export certain hardware measurements from them.

Upvotes: 0

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