[ofa-general] Re: [PATCH draft, untested] ehca srq emulation (for IPoIB CM)

[Michael S. Tsirkin]

> Pushing the changes into the driver is a potential maintenance
> nightmare. How does one keep changes across layers in sync?

We have different definitions of "across layers": in my code everything is kept
inside ehca. I call it a maintenance nightmare when there's code in IPoIB that
only ehca owners can test.

> That was the reason I strived to use common code in the NOSRQ case; at
> least  as much as possible and all of it in IPoIB.

And you ended up with a bigger patch.

> In the emulation approach by apportioning off WRs across QPs, we will be
> sacrificing performance by dropping packets or returning an RNR on a
> really busy QP. As I see it, the alternative is to allocate a really big
> SRQ, even when there are very few QPs and wasting a lot of the unused WRs.

As I said, there are obvious performance optimisatons to implement.
We can later add code in IPoIB that, for very large SRQ size,
will post WRs on demand. But at least that will be common code
that everyone can test.

-- 
MST