On Mon, 2009-01-12 at 18:13 +0200, Avi Kivity wrote: > One thing that worries me here is that the spinners will spin on a > memory location in struct mutex, which means that the cacheline holding > the mutex (which is likely to be under write activity from the owner) > will be continuously shared by the spinners, slowing the owner down when > it needs to unshare it. One way out of this is to spin on a location in > struct mutex_waiter, and have the mutex owner touch it when it schedules > out.
Yeah, that is what pure MCS locks do -- however I don't think its a feasible strategy for this spin/sleep hybrid. > So: > - each task_struct has an array of currently owned mutexes, appended to > by mutex_lock() That's not going to fly I think. Lockdep does this but its very expensive and has some issues. We're currently at 48 max owners, and still some code paths manage to exceed that. > - mutex waiters spin on mutex_waiter.wait, which they initialize to zero > - when switching out of a task, walk the mutex list, and for each mutex, > bump each waiter's wait variable, and clear the owner array Which is O(n). > - when unlocking a mutex, bump the nearest waiter's wait variable, and > remove from the owner array > > Something similar might be done to spinlocks to reduce cacheline > contention from spinners and the owner. Spinlocks can use 'pure' MCS locks. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
