Re: [PATCH] infiniband:cma: change iboe packet life time from 18 to 16

[Chao Leng <lengchao@huawei.com>]

Hi, jason
     Gently ping, thank you.

On 2022/11/25 9:00, 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(-)
> 
> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> index cc2222b85c88..2f5b5e6f3d11 100644
> --- a/drivers/infiniband/core/cma.c
> +++ b/drivers/infiniband/core/cma.c
> @@ -47,7 +47,7 @@ MODULE_LICENSE("Dual BSD/GPL");
>   #define CMA_CM_RESPONSE_TIMEOUT 20
>   #define CMA_MAX_CM_RETRIES 15
>   #define CMA_CM_MRA_SETTING (IB_CM_MRA_FLAG_DELAY | 24)
> -#define CMA_IBOE_PACKET_LIFETIME 18
> +#define CMA_IBOE_PACKET_LIFETIME 16
>   #define CMA_PREFERRED_ROCE_GID_TYPE IB_GID_TYPE_ROCE_UDP_ENCAP
>   
>   static const char * const cma_events[] = {
>