How is the local ack timeout for primary path "timeout" in struct ibv_qp_attr calculated? The struct is used in function ibv_query_qp(). What ist the total time until an error is raised? timeout-in-us = 4096 * (2**timeout)

The total time until an error is raised is

real-timeouot * retry_cnt

or

real-timeout * (retry_cnt +1). ?

We get IBV_WC_RETRY_EXC_ERR errors and I want to incrase the timeout or retry numbers as present in struct ibv_qp_attr


struct ibv_qp_attr {

...

uint8_t timeout; /* Local ack timeout for primary path (valid only for RC QPs) */

uint8_t retry_cnt; /* Retry count (valid only for RC QPs) */

...

};

Thank you,

Heiner

Hi,

See this link , it expalis how it is calculated:

https://www.rdmamojo.com/2013/01/19/ibv_query_qp/

Table of timeut values:

timeoutThe minimum timeout that a QP waits for ACK/NACK from remote QP before retransmitting the packet. The value zero is special value which means wait an infinite time for the ACK/NACK (useful for debugging). For any other value of timeout, the time calculation is: usec.

For your convenience, here is the summary of each value and its timeout:0 - infinite

  • 1 - 8.192 usec (0.000008 sec)
  • 2 - 16.384 usec (0.000016 sec)
  • 3 - 32.768 usec (0.000032 sec)
  • 4 - 65.536 usec (0.000065 sec)
  • 5 - 131.072 usec (0.000131 sec)
  • 6 - 262.144 usec (0.000262 sec)
  • 7 - 524.288 usec (0.000524 sec)
  • 8 - 1048.576 usec (0.00104 sec)
  • 9 - 2097.152 usec (0.00209 sec)
  • 10 - 4194.304 usec (0.00419 sec)
  • 11 - 8388.608 usec (0.00838 sec)
  • 12 - 16777.22 usec (0.01677 sec)
  • 13 - 33554.43 usec (0.0335 sec)
  • 14 - 67108.86 usec (0.0671 sec)
  • 15 - 134217.7 usec (0.134 sec)
  • 16 - 268435.5 usec (0.268 sec)
  • 17 - 536870.9 usec (0.536 sec)
  • 18 - 1073742 usec (1.07 sec)
  • 19 - 2147484 usec (2.14 sec)
  • 20 - 4294967 usec (4.29 sec)
  • 21 - 8589935 usec (8.58 sec)
  • 22 - 17179869 usec (17.1 sec)
  • 23 - 34359738 usec (34.3 sec)
  • 24 - 68719477 usec (68.7 sec)
  • 25 - 137000000 usec (137 sec)
  • 26 - 275000000 usec (275 sec)
  • 27 - 550000000 usec (550 sec)
  • 28 - 1100000000 usec (1100 sec)
  • 29 - 2200000000 usec (2200 sec)
  • 30 - 4400000000 usec (4400 sec)
  • 31 - 8800000000 usec (8800 sec)

Relevant only to RC QPs

Regards

Marc