[syslog-ng] syslog CPU usage is sawtooth

We were running syslog-ng with default setting for time_sleep (which is 0) and were consuming approx 50% of a single CPU with syslog-ng. We were concerned about scalability because syslog-ng is single threaded, so we started tuning with time_sleep. We set it to 5 and adjusted related parameters (log_fetch_limit(250), log_fifo_size(1000000)) and now we are seeing a sawtooth CPU usage with a small IO wait (2%) constant on top of the "user" cpu sawtooth. Tooth cpu duration 1 1-10% 25 minutes 2 2-10% 10 minutes 3 3-10% 10 minutes 4 4-10% 10 minutes This pattern repeats. Any ideas on why the sawtooth pattern started appearing only after we adjusted these settings? Just for the curious Redhad 3 - build from source.