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 S1752462AbbBRQgJ (ORCPT <rfc822;w@1wt.eu>);
	Wed, 18 Feb 2015 11:36:09 -0500
Received: from mx1.redhat.com ([209.132.183.28]:46367 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751793AbbBRQgG (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 18 Feb 2015 11:36:06 -0500
Date: Wed, 18 Feb 2015 17:32:56 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Kirill Tkhai <ktkhai@parallels.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>, Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 2/2] [PATCH] sched: Add smp_rmb() in task rq locking
	cycles
Message-ID: <20150218163256.GA29123@redhat.com>
References: <20150217104516.12144.85911.stgit@tkhai> <1424170021.5749.22.camel@tkhai> <20150217121258.GM5029@twins.programming.kicks-ass.net> <20150217130523.GV24151@twins.programming.kicks-ass.net> <20150217160532.GW4166@linux.vnet.ibm.com> <20150217183636.GR5029@twins.programming.kicks-ass.net> <20150217215231.GK4166@linux.vnet.ibm.com> <20150218155334.GA26006@redhat.com> <20150218161112.GB5029@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150218161112.GB5029@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 02/18, Peter Zijlstra wrote:
>
> On Wed, Feb 18, 2015 at 04:53:34PM +0100, Oleg Nesterov wrote:
> > On 02/17, Paul E. McKenney wrote:
> > >
> > >       |   mb  |  wmb  |  rmb  |  rbd  |  acq  |  rel  |  ctl  |
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >    mb |   Y   |       |   Y   |   y   |   Y   |       |   Y   +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >   wmb |   Y   |       |   Y   |   y   |   Y   |       |   Y   +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >   rmb |       |       |       |       |       |       |       +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >   rbd |       |       |       |       |       |       |       +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >   acq |       |       |       |       |       |       |       +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >   rel |   Y   |       |   Y   |   y   |   Y   |       |   Y   +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> > >   ctl |       |       |       |       |       |       |       +
> > >  -----+-------+-------+-------+-------+-------+-------+-------+
> >
> > OK, so "acq" can't pair with "acq", and I am not sure I understand.
>
> Please consider the table in the context of message passing; that is
> what Paul proposed. Your example from sysvsems, while interesting, would
> not fit the general scenario of message passing.

Ah, yeeees, sorry. Somehow I completely missed that part of Paul's email.

> This too illustrates a problem with that approach, people can't read, so
> they'll pick the wrong table to look at.

At least we know that I certainly can't ;)

Thanks,

Oleg.