[squid-users] low squid performance?

Hello,

I observed have too low performance. On 2x 64bit Xeon 2,8GHz 2GB DDR2, 2x WD
RAPTOR Squid 2.5.STABLE12 can answer max for 120 requests/s.
115 r/s - 97-98% usage of first processor. Second is unusable for squid :/. I
have two cache_dirs (aufs). One pre disk.

aragorn ~ # squid -v
Squid Cache: Version 2.5.STABLE12
configure options: --prefix=/usr --bindir=/usr/bin --exec-prefix=/usr
--sbindir=/usr/sbin --localstatedir=/var --mandir=/usr/share/man
--sysconfdir=/etc/squid --libexecdir=/usr/lib/squid
--enable-auth=basic,digest,ntlm --enable-removal-policies=lru,heap
--enable-digest-auth-helpers=password
--enable-basic-auth-helpers=SASL,PAM,getpwnam,YP,NCSA,SMB,MSNT,multi-domain-NTLM,winbind
--enable-external-acl-helpers=ip_user,unix_group,wbinfo_group,winbind_group
--enable-ntlm-auth-helpers=SMB,fakeauth,no_check,winbind
--enable-linux-netfilter --enable-ident-lookups --enable-useragent-log
--enable-cache-digests --enable-delay-pools --enable-referer-log
--enable-truncate --enable-arp-acl --with-pthreads --with-large-files
--enable-htcp --enable-carp --enable-poll --disable-follow-x-forwarded-for
--host=x86_64-pc-linux-gnu --disable-snmp --enable-ssl --enable-underscores
--enable-storeio='ufs,diskd,coss,aufs,null' --enable-async-io

from config:
cache_mem 512MB

aragorn ~ # uname -a
Linux aragorn 2.6.15-gentoo-r5 #1 SMP Thu Feb 16 02:03:43 CET 2006 x86_64
Intel(R) Xeon(TM) CPU 2.80GHz GenuineIntel GNU/Linux

glibc-2.3.90.20060207 with NPTL

Can I do something to improve preformance?

-- 
Tomasz Kolaj