Re: [RFC] sched: implement the exclusive wait queue as a LIFO queue

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Apr 28, 2010 at 04:23:52PM +0800, Changli Gao wrote:
> On Wed, Apr 28, 2010 at 4:15 PM, Yong Zhang <yong.zhang@windriver.com> wrote:
> >
> > What do you mean "we don't need these processes"?
> 
> If the work is less than the workers, we don't need the workers at the
> tail of the exculsive list.

Have you checked how exclusive waitqueues are even used?

> > So some processs(at the tail of exclusive list)will be treated abnormally
> > and it will sleep for a long time, is this reasonable?
> >
> 
> If there isn't enough work to be done, we'd better not disrupt them
> and  leave them sleeping forever to keep the scheduler happier. Do we
> have reason to keep fair to all the workers? Does it have benefit?

How about starving lock contenders?  See wait_on_bit_lock() and grep
for the users e.g.