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List:       linux-rdma
Subject:    RE: [PATCH] infiniband:cma: change iboe packet life time from 18 to 16
From:       Suri Shelvapille <suri () vcinity ! io>
Date:       2022-12-22 16:35:17
Message-ID: DM6PR03MB4907B39444E17BE854927F3DB9E89 () DM6PR03MB4907 ! namprd03 ! prod ! outlook ! com
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Is it possible to make this parameter tunable? In pure IB fabrics I believe you \
can....

-----Original Message-----
From: Jason Gunthorpe <jgg@nvidia.com>
Sent: Wednesday, December 7, 2022 6:49 PM
To: Chao Leng <lengchao@huawei.com>
Cc: leon@kernel.org; linux-rdma@vger.kernel.org
Subject: Re: [PATCH] infiniband:cma: change iboe packet life time from 18 to 16

On Fri, Nov 25, 2022 at 09:00:26AM +0800, Chao Leng wrote:
> The ack timeout retransmission time is affected by the following two
> factors: one is packet life time, another is the HCA processing time.
> Now the default packet lifetime(CMA_IBOE_PACKET_LIFETIME) is 18.
> That means the minimum ack timeout is 2 seconds(2^(18+1)*4us=2.097seconds).
> The packet lifetime means the maximum transmission time of packets on
> the network, 2 seconds is too long.
> Assume the network is a clos topology with three layers, every packet
> will pass through five hops of switches. Assume the buffer of every
> switch is 128MB and the port transmission rate is 25 Gbit/s, the
> maximum transmission time of the packet is 200ms(128MB*5/25Gbit/s).
> Add double redundancy, it is less than 500ms.
> So change the CMA_IBOE_PACKET_LIFETIME to 16, the maximum transmission
> time of the packet will be about 500+ms, it is long enough.
> 
> Signed-off-by: Chao Leng <lengchao@huawei.com>
> ---
> drivers/infiniband/core/cma.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Applied to for-next, thanks

Jason

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