Re: [PATCH 2/2] rxe: correctly calculate iCRC for unaligned payloads

From: Leon Romanovsky <leon@kernel.org>
To: Doug Ledford <dledford@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
	Steve Wise <larrystevenwise@gmail.com>,
	linux-rdma@vger.kernel.org, 3100102071@zju.edu.cn
Subject: Re: [PATCH 2/2] rxe: correctly calculate iCRC for unaligned payloads
Date: Wed, 11 Dec 2019 07:59:50 +0200	[thread overview]
Message-ID: <20191211055950.GQ67461@unreal> (raw)
In-Reply-To: <c20696208c239bd11621ad3101735255738bcc97.camel@redhat.com>

On Tue, Dec 10, 2019 at 11:24:21PM -0500, Doug Ledford wrote:
> On Tue, 2019-12-10 at 08:54 +0200, Leon Romanovsky wrote:
> > On Mon, Dec 09, 2019 at 02:07:06PM -0500, Doug Ledford wrote:
> > >
> > > I've taken these two patches into for-rc (with fixups to the commit
> > > message on the second, as well as adding a Fixes: tag on the
> > > second).
> > >
> > > I stand by what I said about not needing a compatibility flag or
> > > module
> > > option for the user to set.  However, that isn't to say that we
> > > can't
> > > autodetect old soft-RoCE peers.  If we get a packet that fails CRC
> > > and
> > > has pad bytes, then re-run the CRC without the pad bytes and see if
> > > it
> > > matches.  If it does, we could A) mark the current QP as being to an
> > > old
> > > soft-RoCE device (causing us to send without including the pad bytes
> > > in
> > > the CRC) and B) allocate a struct old_soft_roce_peer and save the
> > > guid
> > > into that struct and then put that struct on a list that we then
> > > search
> > > any time we are creating a new queue pair and if the new queue pair
> > > goes
> > > to a guid in the list, then we immediately flag that qp as being to
> > > an
> > > old soft roce device and get the right behavior.  It would slow down
> > > qp
> > > creation somewhat due to the list search, but probably not enough to
> > > worry about.  No one will be doing a 1,000 node cluster MPI job over
> > > soft-RoCE, so we should never notice the list length causing search
> > > problems.  A patch to do something like that would be welcome.
> >
> > Do you find this implementation needed? I see RXE as a development
> > platform and in my view it is unlikely that someone will run RXE in
> > production with mixture of different kernel versions, which requires
> > such compatibility fallback.
>
> It's not a requirement, that's why I took the patches as they were.  It
> would just be a "nice to have".

I see, thanks

>
> --
> Doug Ledford <dledford@redhat.com>
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