Can any one tell me why cond_resched in do_select?

["Wang Nan" <wn.at.lkml@gmail.com>]

Hi, everyone.
I have a question regarding to select system call's code. In
do_select() function, after check each fd in the set, do_select() call
cond_resched(). That line, according to my view, is to reduce the
system freeze time when do the busy querying. But before the call,
when entering into the big loop, do_select call
set_current_state(TASK_INTERRUPTIBLE). Then, if the reschedule really
taken up, the current process will not return unless it catch a
signal, or one of already registered fd send an event.
I've tried in UML. If I replace the cond_resched() into schedule(),
when sys_select() called, the process halt just like I've said.
I don't think there is a bug because this code exist so long time and
no really bad thing happened. I just want to know that, since no
schedule() allowed here, can we delete the useless line?
Thank you.