Bind9 DNS on Solaris 10 x4270 & CPU usage

I have configured a Bind9 DNS on a X4270 machine with Solaris10

I am excuting some repformance tests with DNSPERF tool and maximun CPU usage is 23%. I have seen with
prstat -L -p PID
that named process usses only 2 of the 8 available CPU at the same time although threads for all CPUs exist.

Any idea why this happens and how can I change it? I want to reach at least 70%.

Maybe the load your generating can be handled with 2 CPUs. is your performance test multi-threaded? Make sure it is at least 8-wide. It takes an intense sustained load to max 6+ CPUs

I use 2 vistual test-machines (2 CPUs )to send DNS messages to my DNS. I also use a Netra210 test- machine (on more CPU). I can get 23% with one machine. The strange thing is thar CPU load is not increase if I run DNSperf in 3 all machines. Not even if I run DNSperf locally on my DNS.