linux-kernel - Can any one tell me why cond_resched in do

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Message-ID: <14344f930801231101w3906aeaey88034e0fa8fa3f36@mail.gmail.com>
Date:	Thu, 24 Jan 2008 03:01:53 +0800
From:	"Wang Nan" <wn.at.lkml@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Can any one tell me why cond_resched in do_select?

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.
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