Re: [PATCH for-rc 1/2] IB/hfi1: Avoid excessive retry for TID RDMA READ request

[Doug Ledford <dledford@redhat.com>]

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On Fri, 2019-10-04 at 16:40 -0400, Dennis Dalessandro wrote:
> From: Kaike Wan <kaike.wan@intel.com>
> 
> A TID RDMA READ request could be retried under one of the following
> conditions:
> - The RC retry timer expires;
> - A later TID RDMA READ RESP packet is received before the next
>   expected one.
> For the latter, under normal conditions, the PSN in IB space is used
> for comparison. More specifically, the IB PSN in the incoming TID RDMA
> READ RESP packet is compared with the last IB PSN of a given TID RDMA
> READ request to determine if the request should be retried. This is
> similar to the retry logic for noraml RDMA READ request.
> 
> However, if a TID RDMA READ RESP packet is lost due to congestion,
> header suppresion will be disabled and each incoming packet will raise
> an interrupt until the hardware flow is reloaded. Under this
> condition,
> each packet KDETH PSN will be checked by software against r_next_psn
> and a retry will be requested if the packet KDETH PSN is later than
> r_next_psn. Since each TID RDMA READ segment could have up to 64
> packets and each TID RDMA READ request could have many segments, we
> could make far more retries under such conditions, and thus leading to
> RETRY_EXC_ERR status.
> 
> This patch fixes the issue by removing the retry when the incoming
> packet KDETH PSN is later than r_next_psn. Instead, it resorts to
> RC timer and normal IB PSN comparison for any request retry.
> 
> Fixes: 9905bf06e890 ("IB/hfi1: Add functions to receive TID RDMA READ
> response")
> Cc: <stable@vger.kernel.org>
> Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
> Signed-off-by: Kaike Wan <kaike.wan@intel.com>
> Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>

Thanks, applied to for-rc.

-- 
Doug Ledford <dledford@redhat.com>
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