linux-kernel - Re: "Verifying and Optimizing Compact NUMA-Aware Locks on Weak Memory Models"

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Date:   Sat, 27 Aug 2022 01:47:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alan Stern <stern@...land.harvard.edu>
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 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.

There were a few 'funny' uarchs that were broken, see for example commit
a30718868915f.