[$] Extending time slices for user-space locks

Steven Rostedt recently posteda patch set that could help improve the performance of certain user-spaceapplications by giving the scheduler more context about when they are safe tointerrupt. The patch set lets programs request a small grace windowbefore they can be interrupted so that they can relinquish any locks, decreasing theamount of time that other threads have to spend waiting. Rostedt sharedperformance numbers suggesting that the patch might cut the amount of time spentacquiring locks in half for some programs - although, since his test wasspecifically tuned for this case, real-world projects should expect a somewhatless dramatic improvement. The change received some pushback from schedulermaintainer Peter Zijlstra, who objected to the patch set's approach.