linux-kernel - Re: [RFC][PATCH 3/3] locking/qspinlock: Optimize for x86

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Message-ID: <20180927075935.GA4889@hirez.programming.kicks-ass.net>
Date:   Thu, 27 Sep 2018 09:59:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     will.deacon@....com, mingo@...nel.org,
        linux-kernel@...r.kernel.org, longman@...hat.com,
        tglx@...utronix.de
Subject: Re: [RFC][PATCH 3/3] locking/qspinlock: Optimize for x86

On Thu, Sep 27, 2018 at 09:47:48AM +0200, Andrea Parri wrote:
> > LKMM in particular does _NOT_ deal with mixed sized atomics _at_all_.
> 
> True, but it is nothing conceptually new to deal with: there're Cat
> models that handle mixed-size accesses, just give it time.

Sure, but until that time I must not rely on (and thus not use) LKMM for
qspinlock things.

So while your argument about coherence might be true -- I'll have to
think about it; litmus tests are out the window.