On 6/4/19 1:02 PM, Peter Zijlstra wrote: > On Tue, Jun 04, 2019 at 11:47:21AM -0400, Waiman Long wrote: >> On 6/4/19 5:45 AM, Peter Zijlstra wrote: >>> On Mon, May 20, 2019 at 04:59:16PM -0400, Waiman Long wrote: >>>> With separate count and owner, there are timing windows where the two >>>> values are inconsistent. That can cause problem when trying to figure >>>> out the exact state of the rwsem. For instance, a RT task will stop >>>> optimistic spinning if the lock is acquired by a writer but the owner >>>> field isn't set yet. That can be solved by combining the count and >>>> owner together in a single atomic value. >>> I just realized we can use cmpxchg_double() here (where available of >>> course). >> Does the 2 doubles need to be 128-bit aligned to use cmpxchg_double()? I >> don't think we can guarantee that unless we explicitly set this alignment. > It does :/ and yes, we'd need to play games with __align(2*sizeof(long)) > and such.
So do you want this as an option now as it will be x86 specific? Or we can do that as a follow-up if we want to. Cheers, Longman
