linux-kernel - Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu

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Message-ID: <20140809160510.GK5821@linux.vnet.ibm.com>
Date:	Sat, 9 Aug 2014 09:05:10 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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 v3 tip/core/rcu 1/9] rcu: Add call_rcu_tasks()

On Sat, Aug 09, 2014 at 08:44:39AM -0400, Steven Rostedt wrote:
> On Sat, 9 Aug 2014 08:15:14 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> 
> > As for idle tasks, I'm not sure about those, I think that we should say
> > NO to anything that would require waking idle CPUs, push the pain to
> > ftrace/kprobes, we should _not_ be waking idle cpus.
> 
> I agree, but I haven't had a chance to review the patch set (will
> probably do that on Monday, just got back from vacation last week and
> was inundated by other things).

Let me get v5 out first.  I expect to have it out by end of Monday.

>                                 Does the idle waking happen only when
> there's something queued in the call_rcu_tasks()? It should definitely
> not be waking all the time. That's just wrong.
> 
> But if it only wakes when something is queued, it wouldn't be burdening
> anything, unless it is needed.

Indeed, idle waking only happens when there is an RCU-tasks grace period
in progress.  No RCU-tasks grace period, no RCU-tasks idle waking.

							Thanx, Paul

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