netdev - Re: [PATCH v1 net-next 00/15] nvme-tcp receive offloads

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Date:   Thu, 14 Jan 2021 21:21:47 +0200
From:   Boris Pismenny <borispismenny@...il.com>
To:     David Ahern <dsahern@...il.com>, Sagi Grimberg <sagi@...mberg.me>,
        Boris Pismenny <borisp@...lanox.com>, kuba@...nel.org,
        davem@...emloft.net, saeedm@...dia.com, hch@....de, axboe@...com,
        kbusch@...nel.org, viro@...iv.linux.org.uk, edumazet@...gle.com
Cc:     yorayz@...dia.com, boris.pismenny@...il.com, benishay@...dia.com,
        linux-nvme@...ts.infradead.org, netdev@...r.kernel.org,
        ogerlitz@...dia.com
Subject: Re: [PATCH v1 net-next 00/15] nvme-tcp receive offloads



On 14/01/2021 6:47, David Ahern wrote:
> On 1/13/21 6:27 PM, Sagi Grimberg wrote:
>>> Changes since RFC v1:
>>> =========================================
>>> * Split mlx5 driver patches to several commits
>>> * Fix nvme-tcp handling of recovery flows. In particular, move queue
>>> offlaod
>>>    init/teardown to the start/stop functions.
>>
>> I'm assuming that you tested controller resets and network hiccups
>> during traffic right?
> 
> I had questions on this part as well -- e.g., what happens on a TCP
> retry? packets arrive, sgl filled for the command id, but packet is
> dropped in the stack (e.g., enqueue backlog is filled, so packet gets
> dropped)
> 

On re-transmission the HW context's expected tcp sequence number doesn't
match. As a result, the received packet is un-offloaded and software
will do the copy/crc for its data.

As a general rule, if HW context expected sequence numbers don't match,
then there's no offload.