linux-kernel - Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread wakeups

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Date:	Thu, 03 Jul 2014 07:48:40 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, riel@...hat.com, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	sbw@....edu
Subject: Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread
 wakeups

On Wed, 2014-07-02 at 22:21 -0700, Paul E. McKenney wrote: 
> On Thu, Jul 03, 2014 at 05:31:19AM +0200, Mike Galbraith wrote:

> > NO_HZ_FULL is a property of a set of CPUs.  isolcpus is supposed to go
> > away as being a redundant interface to manage a single property of a set
> > of CPUs, but it's perfectly fine for NO_HZ_FULL to add an interface to
> > manage a single property of a set of CPUs.  What am I missing? 
> 
> Well, for now, it can only be specified at build time or at boot time.
> In theory, it is possible to change a CPU from being callback-offloaded
> to not at runtime, but there would need to be an extremely good reason
> for adding that level of complexity.  Lots of "fun" races in there...

Yeah, understood.

(still it's a NO_HZ_FULL wart though IMHO, would be prettier and more
usable if it eventually became unified with cpuset and learned how to
tap-dance properly;)

-Mike

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