[GTALUG] Open CAPI Standard

[Lennart Sorensen]

On Thu, Jan 02, 2020 at 11:36:05PM -0500, Nicholas Krause via talk wrote:
> Greetings,
> I mentioned this to some of you at the meeting in December but IBM and
> others are working
> on creating a new standard to replace PCI express and some of its
> limitations called Open
> CAPI. The current versions is as fast as NVLink at 50GBs in a x16 lane from
> memory which
> future versions being able to hit over 100GBs in the same lane speed and
> 250ms latency
> guaranteed as compared to the 500ms to 750ms in PCI express.
> 
> This is a link:https://opencapi.org/ to anyone who wants to read the spec,
> through you will
> have to give them a email and I believe where you work. Currently POWER is
> the only
> real architecture supporting it through or NVlink for that matter.

In order for that to have any chance of hitting consumer machines it would
have to be much better than PCIe due to not being backwards compatible.

AGP solved the serious bandwidth limitations of PCI that video cards
needed, but was also a single slot for a single purpose and didn't
replace PCI.  PCIe replaced PCI since it was much faster, much easier
to implement, and had future scalability which PCI couldn't have (a
parallel shared bus just isn't going to scale).

Given PCIe is improving over time and stays backwards compatible,
being two the speed or half the latency likely isn't enough to make
anyone bother.

So for special purpose like super computers, both nvlink and opencapi
have good use cases, but I don't expect to see it in my home PC.  It just
doesn't add enough versus PCIe to warrent a change.  PCIe isn't dead end
after all, the way PCI was.

I do find it interesting that AMD, Google, IBM, Mellanox, nvidia, etc
but NOT intel are members.

Of course intel is proposing Compute Express Link (CXL) instead, and
has a few of the opencapi members part of their group too (Like Google
and HP for example and even AMD).  There is also CCIX which is an
extension to PCIe to make it batter for super computers and such.
Given CXL uses PCIe as its base, I actually expect it to have a much
better chance of a future than opencapi.

-- 
Len Sorensen