On Wed, 28 Apr 2010, Changli Gao wrote: > On Wed, Apr 28, 2010 at 5:29 PM, David Howells <dhowells@xxxxxxxxxx> wrote: > > Changli Gao <xiaosuo@xxxxxxxxx> 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
