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

[Chao Leng <lengchao@huawei.com>]

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[] = {
-- 
2.16.4