linux-kernel - Re: [PATCH v2] RDMA/cma: Make CM response timeout and # CM retries configurable

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Message-ID: <20190613234633.GL22901@ziepe.ca>
Date:   Thu, 13 Jun 2019 20:46:33 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Håkon Bugge <haakon.bugge@...cle.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Parav Pandit <parav@...lanox.com>,
        Steve Wise <swise@...ngridcomputing.com>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] RDMA/cma: Make CM response timeout and # CM retries
 configurable

On Thu, Jun 13, 2019 at 07:39:24PM +0200, Håkon Bugge wrote:
> 
> 
> > On 13 Jun 2019, at 19:23, Jason Gunthorpe <jgg@...pe.ca> wrote:
> > 
> > On Thu, Jun 13, 2019 at 06:58:30PM +0200, Håkon Bugge wrote:
> > 
> >> If you refer to the backlog parameter in rdma_listen(), I cannot see
> >> it being used at all for IB.
> >> 
> >> For CX-3, which is paravirtualized wrt. MAD packets, it is the proxy
> >> UD receive queue length for the PF driver that can be construed as a
> >> backlog. 
> > 
> > No, in IB you can drop UD packets if your RQ is full - so the proxy RQ
> > is really part of the overall RQ on QP1.
> > 
> > The backlog starts once packets are taken off the RQ and begin the
> > connection accept processing.
> 
> Do think we say the same thing. If, incoming REQ processing is
> severly delayed, the backlog is #entries in the QP1 receive queue in
> the PF. I can call rdma_listen() with a backlog of a zillion, but it
> will not help.

backlog and queue depth are different things, we shouldn't confuse
them together..

Jason