memcpy vs slice copy

[BCS]

Hello Don,

> BCS wrote:
> 
>> Hello Jarrett,
>> 
>>> I'm actually kind of shocked that given the prevalence of memory
>>> block copy operations that more CPUs haven't implemented it as a
>>> basic instruction.  Yes, RISC is nice, but geez, this seems like a
>>> no-brainer.
>>> 
>> How about memory to memory DMA, Why even make the CPU wait for it to
>> finish?
>> 
> That actually happens, to some extent, on some CPUs. If you get
> everything right, the data only goes to the outermost cache, and never
> reaches the CPU itself.
> 

I was thinking even more aggressive, for instance: I wonder how much more 
silicon it would take to allow copied that happen to be on the same DIMM 
to never even touch the motherboard?

I can think of some cases where this would be very useful (large matrix transposition 
for one would work well if the memory is set up for arbitrary striding)