Messages in this thread | | | Date | Thu, 12 Nov 2015 07:20:42 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() |
| |
On Thu, Nov 12, 2015 at 04:08:22PM +0100, Peter Zijlstra wrote: > On Thu, Nov 12, 2015 at 07:01:49AM -0800, Paul E. McKenney wrote: > > On Thu, Nov 12, 2015 at 03:50:13PM +0100, Peter Zijlstra wrote: > > > On Thu, Nov 12, 2015 at 06:40:04AM -0800, Paul E. McKenney wrote: > > > > I cannot resist suggesting that any lock that interacts with > > > > spin_unlock_wait() must have all relevant acquisitions followed by > > > > smp_mb__after_unlock_lock(). > > > > > > Ha! that would certainly help here. But it would mean that argh64v8 also > > > needs to define that, even though that is already RCsc. > > > > Maybe. It could also be that arm64 avoids the need somehow, for example > > via their RCsc behavior. Their memory model is similar to PPC, but not > > exactly the same. > > > > Will? > > So when I spoke to Will earlier today, we agreed that LDAXR+STXR is > susceptible to the same problem. The STXR will allow loads to pass up > over that store. > > On v8.1, which is using LDADDA, this is not an issue, for as the ACQUIRE > is part of the LOAD, the Read-Modify-Write is indivisible as a whole, > and therefore a subsequent load has nothing to pass over.
So one approach required for one level of hardware and another for the next level. I can relate to that all too well... :-/
Thanx, Paul
| |