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SubjectRe: [PATCH 2/2] [PATCH] sched: Add smp_rmb() in task rq locking cycles
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.



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