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From: Davide Libenzi on 28 Apr 2010 15:00
On Wed, 28 Apr 2010, Changli Gao wrote:

> On Wed, Apr 28, 2010 at 5:29 PM, David Howells <dhowells(a)redhat.com> wrote:
> > Changli Gao <xiaosuo(a)gmail.com> wrote:
> >
> >> 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?
> >
> > You've made one important assumption: the processes on the wait queue are
> > sleeping waiting to service things... but what if the wait queue governs
> > access to a resource, and all the processes on that wait queue need access to
> > that resource to do things?  Some of the processes waiting for it may never
> > get a go, and so necessary work may be left undone.
> >
>
> You are right. I made the wrong assumption. But we indeed need some
> primitive to add wait_queue at the head of the wait_queue_head, and I
> know epoll needs it, at least.
>
> fs/eventpoll.c: 1443.
> wait.flags |= WQ_FLAG_EXCLUSIVE;
> __add_wait_queue(&ep->wq, &wait);

I'm not sure one user deserves a new function, but like it has been
noticed, the patch for that should eventually be totally isolated from
other bits.


- Davide

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