From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1161085AbcANTmf (ORCPT <rfc822;w@1wt.eu>);
	Thu, 14 Jan 2016 14:42:35 -0500
Received: from [195.59.15.196] ([195.59.15.196]:11439 "EHLO
	mailapp01.imgtec.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org
	with ESMTP id S1754194AbcANTmb (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 14 Jan 2016 14:42:31 -0500
Message-ID: <5697FA0A.6040601@imgtec.com>
Date: Thu, 14 Jan 2016 11:42:02 -0800
From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0
MIME-Version: 1.0
To: <paulmck@linux.vnet.ibm.com>, Will Deacon <will.deacon@arm.com>
CC: Peter Zijlstra <peterz@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>, <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, <linux-arch@vger.kernel.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        <virtualization@lists.linux-foundation.org>,
        Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@zytor.com>, Joe Perches <joe@perches.com>,
        David Miller <davem@davemloft.net>, <linux-ia64@vger.kernel.org>,
        <linuxppc-dev@lists.ozlabs.org>, <linux-s390@vger.kernel.org>,
        <sparclinux@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
        <linux-metag@vger.kernel.org>, <linux-mips@linux-mips.org>,
        <x86@kernel.org>, <user-mode-linux-devel@lists.sourceforge.net>,
        <adi-buildroot-devel@lists.sourceforge.net>,
        <linux-sh@vger.kernel.org>, <linux-xtensa@linux-xtensa.org>,
        <xen-devel@lists.xenproject.org>, "Ralf Baechle" <ralf@linux-mips.org>,
        Ingo Molnar <mingo@kernel.org>, <ddaney.cavm@gmail.com>,
        <james.hogan@imgtec.com>, Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
References: <20160112092711.GP6344@twins.programming.kicks-ass.net> <20160112102555.GV6373@twins.programming.kicks-ass.net> <20160112104012.GW6373@twins.programming.kicks-ass.net> <20160112114111.GB15737@arm.com> <569565DA.2010903@imgtec.com> <20160113104516.GE25458@arm.com> <56969F4B.7070001@imgtec.com> <20160113204844.GV6357@twins.programming.kicks-ass.net> <5696BA6E.4070508@imgtec.com> <20160114120445.GB15828@arm.com> <20160114161604.GT3818@linux.vnet.ibm.com>
In-Reply-To: <20160114161604.GT3818@linux.vnet.ibm.com>
Content-Type: text/plain; charset="windows-1252"; format=flowed
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.20.3.92]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 01/14/2016 08:16 AM, Paul E. McKenney wrote:
> On Thu, Jan 14, 2016 at 12:04:45PM +0000, Will Deacon wrote:
>> On Wed, Jan 13, 2016 at 12:58:22PM -0800, Leonid Yegoshin wrote:
>>> On 01/13/2016 12:48 PM, Peter Zijlstra wrote:
>>>> On Wed, Jan 13, 2016 at 11:02:35AM -0800, Leonid Yegoshin wrote:
>>>>
>>>>> I ask HW team about it but I have a question - has it any relationship with
>>>>> replacing MIPS SYNC with lightweight SYNCs (SYNC_WMB etc)?
>>>> Of course. If you cannot explain the semantics of the primitives you
>>>> introduce, how can we judge the patch.
>>>>
>>>>
>>> You missed a point - it is a question about replacement of SYNC with
>>> lightweight primitives. It is NOT a question about multithread system
>>> behavior without any SYNC. The answer on a latest Will's question lies in
>>> different area.
> What Will said!
>
> Yes, you can cut corners within MIPS architecture-specific code,
> but primitives that are used in the core kernel really do need to
> work as expected.
>
> 							Thanx, Paul
>
>
Absolutelly! Please use SYNC - right now it is not.

An the only point - please use an appropriate SYNC_* barriers instead of 
heavy bold hammer. That stuff was design explicitly to support the 
requirements of Documentation/memory-barriers.txt

It is easy - just use smp_acquire instead of plain smp_mb 
insmp_load_acquire, at least for MIPS.

- Leonid.
- Leonid.