Dear D community (and specifically experts on cache optimization),

I'm a C++ programmer and was waiting for a while to do a project in D.

I'd like to build a cache-optimized decision tree forest library, and I'm debating between D and C++. I'd like to make it similar to atlas, spiral, or other libraries that partially use static optimization with recompilation and meta-programming to cache optimize the code for a specific architecture (specifically the latest xeons / xeon phi). Given D's compile speed and meta-programming, it should be a good fit. The problem that I might encounter is that C++ has a lot more information on the topic, which might be significant bottleneck given I'm just learning cache optimization (from a few papers and "what every programmer should know about memory").

From my understanding, cache optimization mostly involves breaking data and loops into segments that fit in cache, and making sure that commonly used variables (for example sum in sum+=i) stay in cache. Most of this should be solved by statically defining sizes and paddings of blocks to be used for caching. It's more related to low level -- C, from my understanding. Are there any hidden stones?

The other question is how mature is the compiler in terms of optimizing for cache comparing to C++? I think gnu C++ does a few tricks to optimize for cache and there are ways to tweak cache line alignment.

My knowledge on the subject is not yet concrete and limited but I hope this gave an idea of what I'm looking for and you can recommend me a good direction to take.

Best regards,
--Kirill

I would also be curious to see projects in D that involved cache optimization.

On Monday, 10 November 2014 at 19:18:21 UTC, Kirill wrote:
> Dear D community (and specifically experts on cache optimization),
>
> I'm a C++ programmer and was waiting for a while to do a project in D.
>
> I'd like to build a cache-optimized decision tree forest library, and I'm debating between D and C++. I'd like to make it similar to atlas, spiral, or other libraries that partially use static optimization with recompilation and meta-programming to cache optimize the code for a specific architecture (specifically the latest xeons / xeon phi). Given D's compile speed and meta-programming, it should be a good fit. The problem that I might encounter is that C++ has a lot more information on the topic, which might be significant bottleneck given I'm just learning cache optimization (from a few papers and "what every programmer should know about memory").
>
> From my understanding, cache optimization mostly involves breaking data and loops into segments that fit in cache, and making sure that commonly used variables (for example sum in sum+=i) stay in cache.

Assing there isn't more frequently accessed data around, you would want that to stay in a register, not cache.

> Most of this should be solved by statically defining sizes and paddings of blocks to be used for caching. It's more related to low level -- C, from my understanding. Are there any hidden stones?
>
> The other question is how mature is the compiler in terms of optimizing for cache comparing to C++? I think gnu C++ does a few tricks to optimize for cache and there are ways to tweak cache line alignment.
>
> My knowledge on the subject is not yet concrete and limited but I hope this gave an idea of what I'm looking for and you can recommend me a good direction to take.
>
> Best regards,
> --Kirill

D is a good language for this sort of thing. Using various metaprogramming techniques it might even be fun.

Most advice for C(++) will also apply to D w.r.t. cache.

You will probably have to learn assembly and also make use of tools such as cachegrind and perf unless you like trying to optimise blind.

A word of warning: modern CPU caches are complicated and are sometimes difficult to understand w.r.t. performance in specific cases.