Re: [RFC][PATCH v2] sched/rt: Use IPI to trigger RT task push migration instead of pulling

[Peter Zijlstra]

On Wed, Feb 25, 2015 at 12:50:15PM -0500, Steven Rostedt wrote:
> It can't be used for state?
> 
> If one CPU writes "zero", and the other CPU wants to decide if the
> system is in the state to do something, isn't a rmb() fine to use?
> 
> 
> CPU 1:
> 
> 	x = 0;
> 	/* Tell other CPUs they can now do something */
> 	smp_wmb();
> 
> CPU 2:
> 	/* Make sure we see current state of x */
> 	smp_rmb();
> 	if (x == 0)
> 		do_something();
> 
> The above situation is not acceptable?

Acceptable is just not the word. It plain doesn't work that way.

> Otherwise, we fail to be able to do_something() when it is perfectly
> fine to do so.

Can't be helped.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/