Delay_pools in squid3 and 100% cpu usage?

Question

Squid

There is Ubuntu Server 12.10 (running on Intel Xeon E31235 @ 3.20GHz / 16 Gb RAM hardware), distributing Internet to users through the squid proxy server. When shaping via delay_pools is enabled in squid's config, squid loads the processor up to 100%. With delay_pools turned off, everything is fine - the load does not exceed 10-15% with a total channel width of 16 Mbps, there are about 70-90 users simultaneously on the network.
squid version - 3.1.20 (amd64)
Below is part of the config:

acl adm src 192.168.2.99/32<br>
acl users src 192.168.0.0/16<br>
delay_pools 2<br>
delay_class 1 1<br>
delay_class 2 3<br>
delay_access 1 allow adm<br>
delay_access 1 deny all<br>
delay_access 2 allow users<br>
delay_access 2 deny all<br>
http_access allow users<br>
http_access allow adm<br>
http_access deny all<br>
delay_parameters 1 -1/-1<br>
delay_parameters 2 250000/250000 125000/125000 125000/125000<br>

What could be the reason for high CPU usage by squid?

Answer 1

Update Squid.