[openib-general] [RFC] [PATCH v2] rdma/ib_cm: fix APM support
Michael S. Tsirkin
mst at mellanox.co.il
Wed Nov 8 01:47:39 PST 2006
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
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