linux-kernel - Re: [PATCH 2/2] [PATCH] sched: Add smp

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Message-ID: <20150218192345.GE5745@linux.vnet.ibm.com>
Date:	Wed, 18 Feb 2015 11:23:45 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Kirill Tkhai <ktkhai@...allels.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 2/2] [PATCH] sched: Add smp_rmb() in task rq locking
 cycles

On Wed, Feb 18, 2015 at 05:32:56PM +0100, Oleg Nesterov wrote:
> 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 ;)

Nobody can!  ;-)

							Thanx, Paul

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