memcpy vs slice copy

[BCS]

Hello Jarrett,

> On Mon, Mar 16, 2009 at 3:29 PM, BCS <none at anon.com> wrote:
> 
>>> 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?
>> 
> Sure, then you have to worry about waiting for the *DMA* to finish. If
> it's a copy whose result is largely unimportant to the
> immediately-following code (copying a backbuffer into a frontbuffer,
> for example), it doesn't matter.  But for copying large value types,
> I'd think it's pretty important that the copy is semantically atomic.
> 

As long as either the CPU can voluntarily block or the MMU can block access 
until the DMA is done then it's a free gain in that the CPU can do /something/ 
that it wouldn't be able to otherwise.