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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Will Deacon <will.deacon@arm.com>,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Rich Felker <dalias@libc.org>,
	David Howells <dhowells@redhat.com>,
	Daniel Lustig <dlustig@nvidia.com>,
	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>,
	Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH 01/20] asm-generic/mmiowb: Add generic implementation of mmiowb() tracking
Date: Sat, 2 Mar 2019 18:18:50 -0800	[thread overview]
Message-ID: <CAHk-=whxaYGTmHyoWeegL=ihHMDW_FJehUJVN_nP++Su=foL+g@mail.gmail.com> (raw)
In-Reply-To: <1551575210.6lwpiqtg5k.astroid@bobo.none>

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?

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.

Plain wmb() was only guaranteed to order regular memory against each
other (mostly useful for dma) on some of these platforms, because they
had such broken IO synchronization.

So mmiowb() is not a new name. It's been around for a while, and the
people who wanted it have happily become irrelevant. Will is making it
go away, but the name remains for historical reasons, even if Will's
new acronym explanation for the name is much better ;)

                Linus

WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Will Deacon <will.deacon@arm.com>,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Rich Felker <dalias@libc.org>,
	David Howells <dhowells@redhat.com>,
	Daniel Lustig <dlustig@nvidia.com>,
	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>,
	Yoshinori Sato <ysato@users.sourceforge>
Subject: Re: [PATCH 01/20] asm-generic/mmiowb: Add generic implementation of mmiowb() tracking
Date: Sat, 2 Mar 2019 18:18:50 -0800	[thread overview]
Message-ID: <CAHk-=whxaYGTmHyoWeegL=ihHMDW_FJehUJVN_nP++Su=foL+g@mail.gmail.com> (raw)
In-Reply-To: <1551575210.6lwpiqtg5k.astroid@bobo.none>

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?

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.

Plain wmb() was only guaranteed to order regular memory against each
other (mostly useful for dma) on some of these platforms, because they
had such broken IO synchronization.

So mmiowb() is not a new name. It's been around for a while, and the
people who wanted it have happily become irrelevant. Will is making it
go away, but the name remains for historical reasons, even if Will's
new acronym explanation for the name is much better ;)

                Linus

  reply	other threads:[~2019-03-03  2:27 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-01 14:03 [PATCH 00/20] Remove Mysterious Macro Intended to Obscure Weird Behaviours (mmiowb()) Will Deacon
2019-03-01 14:03 ` [PATCH 01/20] asm-generic/mmiowb: Add generic implementation of mmiowb() tracking Will Deacon
2019-03-03  1:43   ` Nicholas Piggin
2019-03-03  2:18     ` Linus Torvalds [this message]
2019-03-03  2:18       ` Linus Torvalds
2019-03-03  3:34       ` Nicholas Piggin
2019-03-03  3:34         ` Nicholas Piggin
     [not found]         ` <CAHk-=whVN58nWh29jvXx+X-Yx9dCC6BeAZOtKak+d01y_UVg=A@mail.gmail.com>
2019-03-03 10:05           ` Nicholas Piggin
2019-03-03 10:05             ` Nicholas Piggin
2019-03-03 18:48             ` Linus Torvalds
2019-03-03 18:48               ` Linus Torvalds
2019-03-05  0:21               ` Nicholas Piggin
2019-03-05  0:21                 ` Nicholas Piggin
2019-03-05  0:33                 ` Linus Torvalds
2019-03-05  0:33                   ` Linus Torvalds
2019-03-03  9:26     ` Michael Ellerman
2019-03-03 10:07       ` Nicholas Piggin
2019-03-04  1:01         ` Michael Ellerman
2019-03-05  0:21           ` Nicholas Piggin
2019-03-04 10:24     ` Michael Ellerman
2019-03-05  0:19       ` Linus Torvalds
2019-03-05  0:19         ` Linus Torvalds
2019-03-07  0:47         ` Michael Ellerman
2019-03-07  0:47           ` Michael Ellerman
2019-03-07  1:13           ` Linus Torvalds
2019-03-07  1:13             ` Linus Torvalds
2019-03-07  9:13           ` Peter Zijlstra
2019-03-07  9:13             ` Peter Zijlstra
2019-03-01 14:03 ` [PATCH 02/20] arch: Use asm-generic header for asm/mmiowb.h Will Deacon
2019-03-01 14:03   ` Will Deacon
2019-03-01 14:03 ` [PATCH 03/20] mmiowb: Hook up mmiowb helpers to spinlocks and generic I/O accessors Will Deacon
2019-03-03  1:47   ` Nicholas Piggin
2019-03-01 14:03 ` [PATCH 04/20] ARM/io: Remove useless definition of mmiowb() Will Deacon
2019-03-01 14:03 ` [PATCH 05/20] arm64/io: " Will Deacon
2019-03-01 14:03 ` [PATCH 06/20] x86/io: " Will Deacon
2019-03-01 14:03 ` [PATCH 07/20] nds32/io: " Will Deacon
2019-03-01 14:03 ` [PATCH 08/20] m68k/io: " Will Deacon
2019-03-01 14:03 ` [PATCH 09/20] sh/mmiowb: Add unconditional mmiowb() to arch_spin_unlock() Will Deacon
2019-03-01 14:03 ` [PATCH 10/20] mips/mmiowb: " Will Deacon
2019-03-01 22:16   ` Paul Burton
2019-03-01 14:03 ` [PATCH 11/20] ia64/mmiowb: " Will Deacon
2019-03-01 14:03 ` [PATCH 12/20] powerpc/mmiowb: Hook up mmwiob() implementation to asm-generic code Will Deacon
2019-03-02 12:46   ` Michael Ellerman
2019-03-02 12:46     ` Michael Ellerman
2019-03-02 12:46     ` Michael Ellerman
2019-03-01 14:03 ` [PATCH 13/20] riscv/mmiowb: " Will Deacon
2019-03-01 21:13   ` Palmer Dabbelt
2019-03-01 21:13     ` Palmer Dabbelt
2019-03-01 14:03 ` [PATCH 14/20] Documentation: Kill all references to mmiowb() Will Deacon
2019-03-01 14:03 ` [PATCH 15/20] drivers: Remove useless trailing comments from mmiowb() invocations Will Deacon
2019-03-01 14:03 ` [PATCH 16/20] drivers: Remove explicit invocations of mmiowb() Will Deacon
2019-03-01 14:03 ` [PATCH 17/20] scsi/qla1280: Remove stale comment about mmiowb() Will Deacon
2019-03-01 14:03 ` [PATCH 18/20] i40iw: Redefine i40iw_mmiowb() to do nothing Will Deacon
2019-03-01 14:03 ` [PATCH 19/20] net/ethernet/silan/sc92031: Remove stale comment about mmiowb() Will Deacon
2019-03-01 14:03 ` [PATCH 20/20] arch: Remove dummy mmiowb() definitions from arch code Will Deacon
2019-03-01 16:41 ` [PATCH 00/20] Remove Mysterious Macro Intended to Obscure Weird Behaviours (mmiowb()) Linus Torvalds
2019-03-02 12:56   ` Michael Ellerman

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