Re: [for-next PATCH] infiniband:cma: add a parameter for the packet lifetime

[Chao Leng <lengchao@huawei.com>]

On 2022/11/22 22:08, Jason Gunthorpe wrote:
> On Tue, Nov 22, 2022 at 05:02:06PM +0800, Chao Leng wrote:
>> 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, the maximum transmission time of packets is closely
>> related to the network. 2 seconds is too long for simple lossless networks.
>> The packet lifetime should allow the user to adjust according to the
>> network situation.
>> So add a parameter for the packet lifetime.
>>
>> Signed-off-by: Chao Leng <lengchao@huawei.com>
>> ---
>>   drivers/infiniband/core/cma.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
>> index cc2222b85c88..8e2ff5d610e3 100644
>> --- a/drivers/infiniband/core/cma.c
>> +++ b/drivers/infiniband/core/cma.c
>> @@ -50,6 +50,10 @@ MODULE_LICENSE("Dual BSD/GPL");
>>   #define CMA_IBOE_PACKET_LIFETIME 18
>>   #define CMA_PREFERRED_ROCE_GID_TYPE IB_GID_TYPE_ROCE_UDP_ENCAP
>>   
>> +static unsigned char cma_packet_lifetime = CMA_IBOE_PACKET_LIFETIME;
>> +module_param_named(packet_lifetime, cma_packet_lifetime, byte, 0644);
>> +MODULE_PARM_DESC(packet_lifetime, "max transmission time of the packet");
> 
> No new module parameters
> 
> Maybe something in netlink would be appropriate, I'm not sure how
> best to deal with this.
> 
> Really, the entire retransmit strategy in CM is not suitable for
> ethernet networks, this is just one symptom.
What do you think to change the CMA_IBOE_PACKET_LIFETIME to 16.
The maximum transmission time of packets will be about 500+ms,
I think this is long enough for RoCE networks.
2 seconds is too long to my honest.