ok, i wait wait wait and figured out myself. matlab documentation is wrong. here is what is in this document, http://www.mathworks.com/help/matlab/ref/pcode.html
"...pcode(fun) encrypts the code in fun.m and produces a file called fun.p, known as a P-file. ..."
In fact, this fun has to be a string of directory or full file name,
>> modeldev = '/home/jincao/pcodedir/';
>> pcode(modeldev,'-inplace');
this worked.