[mistwang]

Looks like PHP processes are going into a infinite loop or some thing very CPU intensive.

Cpu0 : 7.5%us, 5.5%sy, 87.1%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu1 : 5.5%us, 6.0%sy, 88.5%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu2 : 4.0%us, 2.5%sy, 93.5%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu3 : 11.4%us, 7.5%sy, 80.1%ni, 0.0%id, 0.0%wa, 0.0%hi, 1.0%si, 0.0%st

CPU idle is 0 percent

30845 nobody 17 1 115m 11m 5680 R 47.8 0.1 0:59.91 lsphp5

try strace the PHP processes on top of the "top" output
do

strace -tt -T -p 30845

to find out what is the PHP process doing.