Is 2X faster large memcpy interesting?

[Christopher Wright]

Don wrote:
> The next D2 runtime will include my cache-size detection code. This 
> makes it possible to write a cache-aware memcpy, using (for example) 
> non-temporal writes when the arrays being copied exceed the size of the 
> largest cache.
> In my tests, it gives a speed-up of approximately 2X in such cases.
> The downside is, it's a fair bit of work to implement, and it only 
> affects extremely large arrays, so I fear it's basically irrelevant (It 
> probably won't help arrays < 32K in size). Do people actually copy 
> megabyte-sized arrays?
> Is it worth spending any more time on it?

I don't use large arrays very often. When I do, I would not copy them if 
I could avoid it. Usually, either I keep catenating to an array until a 
certain point, then I only ever need to read from it, with no copying 
ever necessary. So I would rarely, if ever, benefit from this.