On Fri, Feb 29, 2008 at 01:03:16PM -0800, Christoph Lameter wrote: > That means we need both the anon_vma locks and the i_mmap_lock to become > semaphores. I think semaphores are better than mutexes. Rik and Lee saw > some performance improvements because list can be traversed in parallel > when the anon_vma lock is switched to be a rw lock.
The improvement was with a rw spinlock IIRC, so I don't see how it's related to this. Perhaps the rwlock spinlock can be changed to a rw semaphore without measurable overscheduling in the fast path. However theoretically speaking the rw_lock spinlock is more efficient than a rw semaphore in case of a little contention during the page fault fast path because the critical section is just a list_add so it'd be overkill to schedule while waiting. That's why currently it's a spinlock (or rw spinlock). > Sounds like we get to a conceptually clean version here? I don't have a strong opinion if it should become a semaphore unconditionally or only with a CONFIG_XPMEM=y. But keep in mind preempt-rt runs quite a bit slower, or we could rip spinlocks out of the kernel in the first place ;) ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
