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

From: Doug Ledford <dledford@redhat.com>
To: Leon Romanovsky <leon@kernel.org>
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: Tue, 10 Dec 2019 23:24:21 -0500	[thread overview]
Message-ID: <c20696208c239bd11621ad3101735255738bcc97.camel@redhat.com> (raw)
In-Reply-To: <20191210065410.GK67461@unreal>

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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".

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

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