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Message-ID: <20150226074559.GP21418@twins.programming.kicks-ass.net>
Date: Thu, 26 Feb 2015 08:45:59 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Clark Williams <williams@...hat.com>,
linux-rt-users <linux-rt-users@...r.kernel.org>,
Mike Galbraith <umgwanakikbuti@...il.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Jörn Engel <joern@...estorage.com>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC][PATCH v2] sched/rt: Use IPI to trigger RT task push
migration instead of pulling
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.
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