Messages in this thread | | | Date | Fri, 26 Aug 2022 18:23:24 +0200 | From | Peter Zijlstra <> | Subject | Re: "Verifying and Optimizing Compact NUMA-Aware Locks on Weak Memory Models" |
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On Fri, Aug 26, 2022 at 05:48:12AM -0700, Paul E. McKenney wrote: > Hello! > > I have not yet done more than glance at this one, but figured I should > send it along sooner rather than later. > > "Verifying and Optimizing Compact NUMA-Aware Locks on Weak > Memory Models", Antonio Paolillo, Hernán Ponce-de-León, Thomas > Haas, Diogo Behrens, Rafael Chehab, Ming Fu, and Roland Meyer. > https://arxiv.org/abs/2111.15240 > > The claim is that the queued spinlocks implementation with CNA violates > LKMM but actually works on all architectures having a formal hardware > memory model. > > Thoughts?
So the paper mentions the following defects:
- LKMM doesn't carry a release-acquire chain across a relaxed op
- some babbling about a missing propagation -- ISTR Linux if stuffed full of them, specifically we require stores to auto propagate without help from barriers
- some handoff that is CNA specific and I've not looked too hard at presently.
I think we should address that first one in LKMM, it seems very weird to me a RmW would break the chain like that. Is there actual hardware that doesn't behave?
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