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Date:   Sun, 03 Mar 2019 13:34:36 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH 01/20] asm-generic/mmiowb: Add generic implementation of
 mmiowb() tracking
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Andrea Parri <andrea.parri@amarulasolutions.com>,
        Arnd Bergmann <arnd@arndb.de>,
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        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
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        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Tony Luck <tony.luck@intel.com>,
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        Yoshinori Sato <ysato@users.sourceforge.jp>
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Linus Torvalds's on March 3, 2019 12:18 pm:
> On Sat, Mar 2, 2019 at 5:43 PM Nicholas Piggin <npiggin@gmail.com> wrote:
>>
>> Is there a reason to call this "mmiowb"? We already have wmb that
>> orders cacheable stores vs mmio stores don't we?
>=20
> Sadly no it doesn't. Not on ia64, and people tried to make that the
> new rule because of the platform breakage on what some people thought
> would be a major platform.

Let me try this again, because I was babbling a train of thought=20
continuing from my past mails on the subject.

  Kill mmiowb with fire.

It was added for a niche platform that hasn't been produced for 10
years for a CPU ISA that is no longer being developed. Let's make mb/wmb
great again (aka actually possible for normal people to understand).

If something comes along again that reorders mmios from different CPUs=20
in the IO controller like the Altix did, they implement wmb the slow and=20
correct way. They can add a new faster primitive for the few devices=20
they care about in the couple of perf critical places that matter.

It doesn't have to be done all at once with this series, obviously this=20
is a big improvement on its own. But why perpetuate the nomenclature
and concept for new code added now?=20

Thanks,
Nick

=