linux-kernel - Re: [PATCH rdma-next v2] RDMA/cma: Use ACK timeout for RoCE packetLifeTime

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Date:   Thu, 14 Nov 2019 12:48:47 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dag Moxnes <dag.moxnes@...cle.com>
Cc:     dledford@...hat.com, leon@...nel.org, parav@...lanox.com,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH rdma-next v2] RDMA/cma: Use ACK timeout for RoCE
 packetLifeTime

On Wed, Oct 30, 2019 at 01:44:00PM +0100, Dag Moxnes wrote:
> The cma is currently using a hard-coded value, CMA_IBOE_PACKET_LIFETIME,
> for the PacketLifeTime, as it can not be determined from the network.
> This value might not be optimal for all networks.
> 
> The cma module supports the function rdma_set_ack_timeout to set the
> ACK timeout for a QP associated with a connection. As per IBTA 12.7.34
> local ACK timeout = (2 * PacketLifeTime + Local CA’s ACK delay).
> Assuming a negligible local ACK delay, we can use
> PacketLifeTime = local ACK timeout/2
> as a reasonable approximation for RoCE networks.
> 
> Signed-off-by: Dag Moxnes <dag.moxnes@...cle.com>
> ---
>  drivers/infiniband/core/cma.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)

This seems like a reasonable thing to do, applied to for-next

Thanks,
Jason