wordcount VS raikv

Another similar experiment. And has Java included :)

There is a similar great project here [1]. The performance of Java there is super impressive.

[1] https://github.com/juditacs/wordcount

I have a graph for this:

https://github.com/raitechnology/raikv/blob/master/graph/mt_...

The CPU in this case is a Threadripper 3970x, 32 cores, 64 SMT.

My experience is this: When the L3 cache is effective, then the memory latency hiding via memory prefetch works well across SMT threads. If the hashtable load requires a chain walk, the SMT latency hiding is less effective because the calculated prefetch location is not the actual hit. I couldn't get prefetching multiple slots as the load increased to be as effective as prefetching a single slot.

Amusingly, I've done a multi-threaded version of the word counting program in order to test a shm kv store. I needed benchmark that created a lot of cross thread concurrent accesses to keys and I found a blog about this test. My version has serious constraints though, you have to create a shared memory map with enough space to hold all of the keys beforehand, as it doesn't resize the shm kv map as it runs.

This is the source for it:

https://github.com/raitechnology/raikv/blob/master/test/ctes...

The speedup of the multi-threaded version vs the single-threaded version is about linear. The single threaded version uses 2 threads, one to read stdin and one to hash the keys, the 16 threaded version uses one thread to read, 16 to hash.

$ time ctest -t 1 < ~/data/enwiki-p10p30303