[4.0.x] radiusd process CPU spikes at 400% when trying to do DHCP concurrently

[Chaigneau, Nicolas]

Hello,


I've tried latest HEAD (054095b5310d1c7b0994565ddb1d9eda2b45b435).

Now things are... different, but I can't say it's better :/


To sum up:

- Now (054095b5310d1c7b0994565ddb1d9eda2b45b435, December 20):
radiusd does not get stuck at 400% CPU anymore. 
However, it won't go beyond ~60% CPU, and cannot serve more than ~8.8k DHCP Discover/s (using the dummy DHCP virtual server).

- When issue first appeared (7c2b992cc79c5c2cdd2863eb6d91ffb9559dd0a9, November 24):
radiusd CPU rises very rapidly to ~420% CPU. Then after the load test is stopped, radiusd CPU stays forever at exactly 400% CPU, even though it receives no new packet to handle.
(looks like 4 worker threads in a busy loop ?)

- Just before issue appeared (86dec6a917c00d36df0ca5e3a9b04a48e105f488, November 24):
As expected, radiusd CPU usage rises according to the load of packets it has to handle.
It can handle 60k DHCP Discover/s easily (this is not its limit, at this rate it's using ~310% CPU). After the load test is stopped, radiusd CPU goes back to zero.


(just using a "top" to look at the CPU when doing the tests.)



>  I've pushed some fixes which I *hope* will help.  I've broken them down into a series of tiny commits.  So it should be possible to tell (a) which commit fixes things, or (b) which one makes it worse.
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