AHA! I got the idea why /etc/rc.d/ scripts runs very slowly.

PS(1) of NetBSD/pmax runs sluggish.  Because /etc/rc.d/ scripts
fork&exec ps extensively, they are impacted directly by PS(1)
performance. 

Overall, I have strong suspiction of NetBSD/mips TLB management is
designed mistakenly (it behaves as if M68030).  With tagged TLB
machinary, TLB invalidation and synchronization (TBIA, TBIS, and
others) should be avoided at all cost because superfluous invalidation
would kill useful TLB entries which might already be stored in TLB,
and then results in excessive TLBmiss exceptions which could be
avoided after all.

Tohru Nishimura