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Date:   Sun, 03 Mar 2019 20:05:23 +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>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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        David Howells <dhowells@redhat.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        "Maciej W. Rozycki" <macro@linux-mips.org>,
        Ingo Molnar <mingo@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Palmer Dabbelt <palmer@sifive.com>,
        Paul Burton <paul.burton@mips.com>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Tony Luck <tony.luck@intel.com>,
        Will Deacon <will.deacon@arm.com>,
        Yoshinori Sato <ysato@users.sourceforge.jp>
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Linus Torvalds's on March 3, 2019 2:29 pm:
> On Sat, Mar 2, 2019, 19:34 Nicholas Piggin <npiggin@gmail.com> wrote:
>=20
>>
>> It doesn't have to be done all at once with this series, obviously this
>> is a big improvement on its own. But why perpetuate the nomenclature
>> and concept for new code added now?
>>
>=20
> What nomenclature?
>=20
> Nobody will be using mmiowb(). That's the whole point of the patch series=
.
>=20
> It's now an entirely internal name, and nobody cares.

Why even bother with it at all, "internal" or not?  Just get rid of=20
mmiowb, the concept is obsolete.

> And none of this has anything to do with wmb(), since it's about IO being
> ordered across cpu's by spin locks, not by barriers.
>=20
> So I'm not seeing what you're arguing about.

Pretend ia64 doesn't exist for a minute. Now the regular mb/wmb barriers=20
orders IO across CPUs with respect to their cacheable accesses. =20
Regardless of whether that cacheable access is a spin lock, a bit lock,=20
an atomic, a mutex... This is how it was before mmiowb came along.

Nothing wrong with this series to make spinlocks order mmio, but why=20
call it mmiowb? Another patch could rename ia64's mmiowb and then the
name can be removed from the tree completely.

Thanks,
Nick

=