On Sat, Dec 17, 2005 at 07:05:21PM -0500, Lee Revell wrote: > On Sat, 2005-12-17 at 16:43 -0700, Matthew Wilcox wrote: > > I have a better example of something we currently get wrong that I > > haven't heard any RT person worry about yet. If two tasks are sleeping > > on the same semaphore, the one to be woken up will be the first one to > > wait for it, not the highest-priority task. > > > > Obviously, this was introduced by the wake-one semantics. But how to > > fix it? Should we scan the entire queue looking for the best task to > > wake? Should we try to maintain the wait list in priority order? Or > > should we just not care? Should we document that we don't care? ;-) > > It's well known that this is a problem: > > http://developer.osdl.org/dev/robustmutexes/src/fusyn.hg/Documentation/fusyn/fusyn-why.txt
Erm. That paper is talking about user-space semaphores based on futexes. I'm talking about kernel semaphores. At a first glance, fixing futexes would be a very different job from fixing semaphores. BTW, fuqueues? HAHAHAHA.
