linux-kernel - Re: [RFC PATCH] docs/memory-barriers.txt: Rewrite "KERNEL I/O BARRIER EFFECTS" section

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Message-Id: <20190212192405.GU4240@linux.ibm.com>
Date:   Tue, 12 Feb 2019 11:24:05 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH] docs/memory-barriers.txt: Rewrite "KERNEL I/O
 BARRIER EFFECTS" section

On Tue, Feb 12, 2019 at 06:43:54PM +0000, Will Deacon wrote:
> On Mon, Feb 11, 2019 at 12:22:18PM -0800, Paul E. McKenney wrote:
> > On Mon, Feb 11, 2019 at 05:29:48PM +0000, Will Deacon wrote:
> > > The "KERNEL I/O BARRIER EFFECTS" section of memory-barriers.txt is vague,
> > > x86-centric, out-of-date, incomplete and demonstrably incorrect in places.
> > > This is largely because I/O ordering is a horrible can of worms, but also
> > > because the document has stagnated as our understanding has evolved.
> > > 
> > > Attempt to address some of that, by rewriting the section based on
> > > recent(-ish) discussions with Arnd, BenH and others. Maybe one day we'll
> > > find a way to formalise this stuff, but for now let's at least try to
> > > make the English easier to understand.
> > > 
> > > Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>
> > > Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > > Cc: Arnd Bergmann <arnd@...db.de>
> > > Cc: Peter Zijlstra <peterz@...radead.org>
> > > Cc: Andrea Parri <andrea.parri@...rulasolutions.com>
> > > Cc: Daniel Lustig <dlustig@...dia.com>
> > > Cc: David Howells <dhowells@...hat.com>
> > > Cc: Alan Stern <stern@...land.harvard.edu>
> > > cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > > Signed-off-by: Will Deacon <will.deacon@....com>
> > 
> > Hello, Will,
> > 
> > The intent is to replace commit 3f305018dcf3 ("docs/memory-barriers.txt:
> > Enforce heavy ordering for port I/O accesses"), correct?  Either way is
> > fine, just guessing based on the conflicts when applying this one.  ;-)
> 
> Yup, I decided to abandon the old patch:
> 
> http://lkml.kernel.org/r/20190211153043.GC32385@fuggles.cambridge.arm.com

Got it, and thank you for the reminder!

							Thanx, Paul