Re: [PATCH 2/2] [PATCH] sched: Add smp_rmb() in task rq locking cycles
From: Peter Zijlstra
Date: Wed Feb 18 2015 - 08:47:18 EST
On Tue, Feb 17, 2015 at 01:52:31PM -0800, Paul E. McKenney wrote:
> I could do a table per communication style. For example, message
> passing looks like this (give or take likely errors in the table):
>
> Side CPU Top CPU
> -------- -------
> X = 1; r1 = Y;
> <some barrier> <some barrier>
> Y = 1; r2 = X;
>
> assert(r1 == 0 || r2 == 1);
>
>
> | 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 | | | | | | | +
> -----+-------+-------+-------+-------+-------+-------+-------+
>
> Here "Y" says that the barrier pair works, "y" says that it can
> work but requires an artificial dependency, and " " says that
> it does not work.
I would maybe do s/artificial/additional/, the pointer deref in RCU is
not really artificial, is it?
Also, how many communication styles do you envision to enumerate?
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