From: Will Deacon <will.deacon@arm.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"monstr@monstr.eu" <monstr@monstr.eu>,
"dhowells@redhat.com" <dhowells@redhat.com>,
"broonie@linaro.org" <broonie@linaro.org>,
"benh@kernel.crashing.org" <benh@kernel.crashing.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"paulmck@linux.vnet.ibm.com" <paulmck@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH v2 16/18] x86: io: implement dummy relaxed accessor macros for writes
Date: Fri, 23 May 2014 15:57:58 +0100 [thread overview]
Message-ID: <20140523145758.GG21319@arm.com> (raw)
In-Reply-To: <537F60E0.1060307@zytor.com>
On Fri, May 23, 2014 at 03:53:20PM +0100, H. Peter Anvin wrote:
> On 05/23/2014 07:46 AM, Will Deacon wrote:
> >
> > I would like the relaxed accessors to be ordered with respect to each other...
> >
> > What do you think?
> >
>
> I think "I would like" isn't a very good motivation. What are the
> semantics of these things supposed to be? It seems more than a bit odd
> to require them to be ordered with respect to each other and everything
> else (which is what a memory clobber does) and then call them "relaxed".
I suggested some informal semantics in the cover letter:
https://lkml.org/lkml/2014/4/17/269
Basically, if we define relaxed accesses not to be ordered against anything
apart from other accesses (relaxed or otherwise) to the same device, then
they become a tonne cheaper on arm/arm64/powerpc. Currently we have to
include expensive memory barriers in order to synchronise with accesses to
DMA buffers which is rarely needed.
For those requirements, I don't think we need the "memory" clobber for x86,
but would appreciate your views on this.
Will
next prev parent reply other threads:[~2014-05-23 14:58 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-22 16:47 [PATCH v2 00/18] Cross-architecture definitions of relaxed MMIO accessors Will Deacon
2014-05-22 16:47 ` [PATCH v2 01/18] asm-generic: io: implement relaxed accessor macros as conditional wrappers Will Deacon
2014-05-22 16:47 ` [PATCH v2 02/18] microblaze: io: remove dummy relaxed accessor macros Will Deacon
2014-05-22 16:47 ` [PATCH v2 03/18] s390: io: remove dummy relaxed accessor macros for reads Will Deacon
2014-05-22 16:47 ` [PATCH v2 04/18] xtensa: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 05/18] alpha: io: implement relaxed accessor macros for writes Will Deacon
2014-05-22 18:15 ` Richard Henderson
2014-05-22 16:47 ` [PATCH v2 06/18] frv: io: implement dummy " Will Deacon
2014-05-22 16:47 ` [PATCH v2 07/18] cris: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 08/18] ia64: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 09/18] m32r: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 10/18] m68k: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 11/18] mn10300: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 12/18] parisc: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 13/18] powerpc: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 14/18] sparc: " Will Deacon
2014-05-22 18:18 ` Sam Ravnborg
2014-05-23 14:38 ` Will Deacon
2014-05-30 0:10 ` David Miller
2014-05-22 16:47 ` [PATCH v2 15/18] tile: " Will Deacon
2014-05-22 16:47 ` [PATCH v2 16/18] x86: " Will Deacon
2014-05-22 17:15 ` H. Peter Anvin
2014-05-23 14:46 ` Will Deacon
2014-05-23 14:53 ` H. Peter Anvin
2014-05-23 14:57 ` Will Deacon [this message]
2014-05-23 15:20 ` H. Peter Anvin
2014-05-23 15:34 ` Will Deacon
2014-05-23 15:43 ` H. Peter Anvin
2014-05-23 15:56 ` Peter Zijlstra
2014-05-23 16:12 ` H. Peter Anvin
2014-05-23 16:21 ` Peter Zijlstra
2014-05-23 16:31 ` Geert Uytterhoeven
2014-05-23 16:35 ` H. Peter Anvin
2014-05-22 16:47 ` [PATCH v2 17/18] documentation: memory-barriers: clarify relaxed io accessor semantics Will Deacon
2014-05-22 16:47 ` [PATCH v2 18/18] asm-generic: io: define relaxed accessor macros unconditionally Will Deacon
2014-05-25 21:46 ` [PATCH v2 00/18] Cross-architecture definitions of relaxed MMIO accessors Benjamin Herrenschmidt
2014-05-27 19:32 ` Will Deacon
2014-05-27 20:21 ` Benjamin Herrenschmidt
2014-05-27 20:32 ` Will Deacon
2014-05-25 21:47 ` Benjamin Herrenschmidt
2014-05-27 19:34 ` Will Deacon
2014-05-27 20:23 ` Benjamin Herrenschmidt
2014-05-27 20:34 ` Will Deacon
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