i noticed this behaviour from the testprogram that comes with the HawkNL package, namely with the Test_clientserver test.
The server thread of this test program polls the socketgroup with a timeout of 0
count = nlPollGroup(group, NL_READ_STATUS, s, MAX_CLIENTS, 0);
This causes a 100% cpu load of the server thread
If the timeout is changed to e.g. 1 (specified in msec) the cpu-load will drop
count = nlPollGroup(group, NL_READ_STATUS, s, MAX_CLIENTS, 1);
So check the CEL net-testcode for the nlPollGroup method...