futex take much CPU time and cause errors

[lunardancer]

In a bind9 performance testing I monitored one of named threads with strace for a while, and got below message:

[root at dl580-1 root]# strace -p 1797 -c
Process 1797 attached - interrupt to quit
Process 1797 detached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 69.11    5.681319          13    442646    137491 futex
 19.30    1.586145          13    118467           sendmsg
 10.86    0.892565           8    118579        72 recvmsg
  0.72    0.059597           3     23725           gettimeofday
  0.01    0.000738          15        48           write
------ ----------- ----------- --------- --------- ----------------
100.00    8.220364                703465    137563 total

I traced down the futex errors:
There're many sth. like 'futex(0x818f1bc, FUTEX_WAIT, 585151, NULL) = -1 EAGAIN (Resource temporarily unavailable)'. 


At this time the CPU utilization is:
CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle
           total   39.1%    0.0%   39.1%   1.0%    15.9%    0.0%    4.7%
           cpu00   30.5%    0.0%   20.3%   4.2%    44.9%    0.0%    0.0%
           cpu01   39.8%    0.0%   48.3%   0.0%     5.9%    0.0%    5.9%
           cpu02   45.1%    0.0%   41.7%   0.0%     5.9%    0.0%    7.2%
           cpu03   41.1%    0.0%   46.1%   0.0%     6.7%    0.0%    5.9%
Mem:  7997692k av,  298108k used, 7699584k free,       0k shrd,   11956k buff
        49004k active,             190420k inactive
Swap: 2096472k av,       0k used, 2096472k free                  227280k cached

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND
 1795 named     25   0  2960 2960  1892 S    24.9  0.0  29:20   3 named


Do you know what is going on and cause so many system CPU utilization?

thx.