'time the bulding of the kernel'

def build_timed(self, threads, timefile='/dev/null', make_opts='', output='/dev/null'):

    os.chdir(self.build_dir)
    self.set_cross_cc()
    self.clean()
    build_string = ('/usr/bin/time    -o    %s    make    %s    -j    %s    vmlinux' % (timefile, make_opts, threads))
    build_string += ('    >    %s    2>&1' % output)
    print build_string
    utils.system(build_string)
    if (not os.path.isfile('vmlinux')):
        errmsg = 'no    vmlinux    found,    kernel    build    failed'
        raise error.TestError(errmsg)
