strange thread priority displayed in top

It seems top displaying thread priority in kernel strangely.
Look at threads blocked at select() syscall, it is displayed as 96,
it is userland priority: 96 + PZERO = 180.

---
last pid:  4352;  load averages:  0.00,  0.11,  0.08 
                                                              up 
0+00:06:24  16:40:03
138 processes: 2 running, 136 sleeping
CPU states:  0.4% user,  0.0% nice,  0.0% system,  0.0% interrupt, 99.6% 
idle
Mem: 202M Active, 100M Inact, 129M Wired, 4824K Cache, 159M Buf, 559M Free
Swap: 2020M Total, 2020M Free

   PID USERNAME    THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
  1075 davidxu       2  -8    0 53920K 25432K piperd 0   0:01  1.03% 
gnome-terminal
  1020 davidxu       1  96    0 35048K 16344K CPU1   1   0:05  0.00% Xorg
   626 _tor          1   4    0 17256K 11492K kqread 1   0:02  0.00% tor
  1052 davidxu       1  96    0 58916K 27988K select 0   0:01  0.00% 
nautilus
  1053 davidxu       1  96    0 39368K 22504K select 1   0:01  0.00% 
gnome-panel
  1070 davidxu       1  96    0 39416K 21476K select 0   0:01  0.00% 
mixer_applet2
  1061 davidxu       1  96    0 37692K 20716K select 1   0:00  0.00% 
wnck-applet

---

I think the problem is select() uses cv_wait_sig which does not raise
thread priority, but cv_broadcast() has a priority parameter to
raise thread's priorities, however cv_signal() does not have this
parameter, these are inconsitent interfaces. To fix the problem, there
are two ways:
1. pass a priority parameter to cv_init(), and cv_wait(), cv_wait_sig()
    etcs will use the priority, remove priority parameter from
    cv_broadcast().

2. pass a priority parameter to cv_wait(), and cv_wait_sig() etcs.

I prefer the first one.

Regards,
David Xu