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

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Message-ID: <20191029195101.GA1654@ziepe.ca>
Date:   Tue, 29 Oct 2019 16:51:01 -0300
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] RDMA/cma: Use ACK timeout for RoCE
 packetLifeTime

On Fri, Oct 25, 2019 at 01:42:01PM +0200, 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>
> Change-Id: I200eda9d54829184e556c3c55d6a8869558d76b2

Please don't send Change-Id to the public lists. Run checkpatch before
sending.

Otherwise this seems reasonable to me..

Jason