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Date: Sat, 27 Aug 2022 12:05:33 -0400 From: Alan Stern <stern@...land.harvard.edu> To: Peter Zijlstra <peterz@...radead.org> Cc: "Paul E. McKenney" <paulmck@...nel.org>, parri.andrea@...il.com, will@...nel.org, boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr, akiyks@...il.com, dlustig@...dia.com, joel@...lfernandes.org, linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org Subject: Re: "Verifying and Optimizing Compact NUMA-Aware Locks on Weak Memory Models" On Sat, Aug 27, 2022 at 01:47:48AM +0200, Peter Zijlstra wrote: > On Fri, Aug 26, 2022 at 01:10:39PM -0400, Alan Stern wrote: > > > > - some babbling about a missing propagation -- ISTR Linux if stuffed > > > full of them, specifically we require stores to auto propagate > > > without help from barriers > > > > Not a missing propagation; a late one. > > > > Don't understand what you mean by "auto propagate without help from > > barriers". > > Linux hard relies on: > > CPU0 CPU1 > > WRITE_ONCE(foo, 1); while (!READ_ONCE(foo)); > > making forward progress. Indeed yes. As far as I can tell, this requirement is not explicitly mentioned in the LKMM, although it certainly is implicit. I can't even think of a way to express it in a form Herd could verify. > There were a few 'funny' uarchs that were broken, see for example commit > a30718868915f. Ha! That commit should be a lesson in something, although I'm not sure what. :-) Alan
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