3.3 microseconds latency for the flash at the memory bus are about 11,000 cycles latency @ 3.3GHz. That is quite a lot compared to a normal DDR latency of about 150 cycles. Of course it's much better than 100 microseconds or about 330,000 cycles for a normal SSD. I would guess that the overhead for a page fault would be around 1000 cycles.
Writing a block device for Linux so that the flash could be used as a cache or ram disk is quite easy (speaking from experience) and I assume that Diablo has already written one.
If Diablo had access to the memory controller inside the main CPU they could even run the DDR as a cache for the flash memory like some giant L4 cache. In such a scenario the DDR ram emulation would make sense...
A page fault is going to cost way way more then 1000 cycles, it's going to be, at bare minimum(for major faults), your storage medium's read latency, so 100 microseconds or more. I'd think in many circumstances hitting a 3.3 microsecond latency to avoid a 100 microsecond latency is def. a good trade. There might be an issue if you have to repeatedly pay that 3.3 microsecond vs. one time the 100 microsecond, but that's getting into things that we can't really know without knowing more specs about the stuff.
And I was more speaking about using it as a blazing fast non-volatile "ram" drive. I know a standard ram drive is simple, but it'd be neat to install os and programs and such onto a drive with 2 order of magnitude better performance then a high-end SSD.
Writing a block device for Linux so that the flash could be used as a cache or ram disk is quite easy (speaking from experience) and I assume that Diablo has already written one.
If Diablo had access to the memory controller inside the main CPU they could even run the DDR as a cache for the flash memory like some giant L4 cache. In such a scenario the DDR ram emulation would make sense...