[openib-general] [RFC] [PATCH v2] rdma/ib_cm: fix APM support

[Michael S. Tsirkin]

Quoting Or Gerlitz <ogerlitz at voltaire.com>:
> > Protocols that rely on RC ACK for reliability guarantees (like SDP), basically
> > do not make it possible to address the hca failure case: you got an ACK, but
> > remote hca could have failed without committing data to memory. So APM failover
> > is a requirement for these. It could be iser does not need APM, fine.
> 
> This is news to me, does your HCA first sends an ACK and only then does 
> the DMA transaction and if needed generates the CQE !?!?!?

I can't tell either way, but why not?
Consider also that DMA write is a posted transaction - HCA gets no indication
when it was committed to memory, so it can not delay the ACK until this occurs.

> and how come APM is the solution to this crazy problem?

If HCA failure is a crazy problem, then what is the sane problem APM does *not* solve?

-- 
MST