[squid-users] squid consuming too much processor/cpu

Squid Cache: Version 2.7.STABLE5(squid-2.7.STABLE5-2.3)
kernel version: 2.6.27 x86_64
CPU: Xeon 2.6 GHz CPU
Memory: 2 GB
/var/cache/squid is ext3, mounted with 'noacl' and 'noatime' options
number of users using this proxy: 160
number of users using simultaneously/concurrently using this proxy: 72

I found that squid is consuming too much cpu, average cpu idle time is
49 only.

I have attached the output 'top -b -n 7', and 'vmstat 1'

below is the output of squid.conf

squid.conf:
---------

http_port 8080
cache_mgr administrator_at_test.com
cache_mem 1024 MB
cache_dir aufs /var/cache/squid 20000 32 256
visible_hostname gateway.test.com
refresh_pattern ^ftp: 1440 20% 10080
refresh_pattern ^gopher: 1440 0% 1440
refresh_pattern -i \.(gif|png|jpg|jpeg|ico)$ 10080 90% 43200
refresh_pattern -i \.(iso|avi|wav|mp3|mp4|mpeg|swf|flv|x-flv)$ 43200 90%
432000
refresh_pattern -i \.(deb|rpm|exe|zip|tar|tgz|ram|rar|bin|ppt|doc|tiff)$
10080 90% 43200
refresh_pattern -i \.index.(html|htm)$ 0 40% 10080
refresh_pattern -i \.(html|htm|css|js)$ 1440 40% 40320
refresh_pattern . 0 40% 40320
cache_swap_low 78
cache_swap_high 90

maximum_object_size_in_memory 100 KB
maximum_object_size 12288 KB

fqdncache_size 2048
ipcache_size 2048

acl myFTP port 20 21
acl ftp_ipes src "/etc/squid/ftp_ipes.txt"
http_access allow ftp_ipes myFTP
http_access deny myFTP

acl porn_deny url_regex "/etc/squid/domains.deny"
http_access deny porn_deny

acl vip src "/etc/squid/vip_ipes.txt"
http_access allow vip

acl entweb url_regex "/etc/squid/entwebsites.txt"
http_access deny entweb

acl mynet src "/etc/squid/allowed_ipes.txt"
http_access allow mynet

please help, why squid is utilizing so much of cpu

-- 
Regards
Muhammad Sharfuddin | NDS Technologies Pvt Ltd | +92-333-2144823