linux-kernel - Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle tasks

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Message-ID: <20140813140705.GO9918@twins.programming.kicks-ass.net>
Date:	Wed, 13 Aug 2014 16:07:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
	oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle
 tasks

On Wed, Aug 13, 2014 at 09:51:32AM -0400, Steven Rostedt wrote:

> I still need to look at the patches, but if this is just for the idle
> case, then we don't need it. The idle case can be solved with a simple
> sched_on_each_cpu(). I need a way to solve waiting for processes to
> finish from a preemption point.
> 
> That's all I want, and if we can remove the "idle" case and document it
> well that it's not covered and a sched_on_each_cpu() may be needed,
> then I'm fine with that.
> 
> 	sched_on_each_cpu(dummy_op);
> 	call_rcu_tasks(free_tramp);

Sure, but why not dtrt and push rcu_idle hooks all the way down into the
idle drivers if and where appropriate?

There isn't _that_ much idle driver code. Also, some stuff should be
cleaned up; we're already calling stop_critical_timings() in the generic
idle code, and then calling it again in the cpuidle drivers.



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