Symptom

Th throughput of ISM module seem to be very low, when ping is issued we observe drops.

Conditions

Though the ping shows drops, ISM module is taking a lot of time to process the packet and respond back with echo reply beyond the time the ping would expect resulting in drops. This issue is observed when fragmented packets hits ISM module, buffer handling of fragment packets is a bit involved activity in ISM as it will wait for the whole packet to be received before it decrypts the packet, while this is happening there is a stray print message which results in context switching of the packet context and take time to complete the decryption activity. Result in delay response which reduces throughput and also gives an application (like ping) the packets are dropped.

Workaround

Disable fragmentation

Further Problem Description