Re: [PATCH] libibverbs/doc: clarify selective signaling (Re: using IBV_SEND_SIGNALED)

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Tue, Nov 30, 2010 at 01:56:13PM +0200, Or Gerlitz wrote:
> Steve Wise wrote:
> > On 11/29/2010 11:34 AM, Robert D. Russell wrote:
> > See section 8.2.1 of the iWARP Verbs draft at:
> > http://tools.ietf.org/html/draft-hilland-rddp-verbs-00#section-8.2.1.
> > The last big paragraph in 8.2.1 spells it all out.
> > There should be a similar requirement in the IBTA IB Verbs specification...
> 
> Yes, I think the below patch to the man page can help people
> understand how to work with the thing

I think the subtly here is that remote completion of a local WR does
not indiciate local completion. This is the only operational case I
can think of that might break the rules.

For instance a protocol that had remote acks for all SENDs might be
tempted to not ever use signaled WR's on the local side - since
receiving the remote ACK SEND must indicate the local SEND WR is
complete. This is the incorrect assumption.

So, I'd suggest this language:

Applications which use selective signaling can only assume that
unsignaled WRs are complete once a completion for a later signaled WR
is received. In practice this means that a signaled WR must be
used periodically, and that the send queue should never be filled with
unsignaled WRs.

Jason
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