linux-kernel - Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call

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Date:	Thu, 8 Mar 2012 11:44:14 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine
 call_srcu()

On Tue, Mar 06, 2012 at 11:47:25AM +0100, Peter Zijlstra wrote:
> On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote:
> > o       The srcu callback is new thing, I hope it is completely preemptible,
> >         even sleepable. It does in this implemetation, I use work_struct
> >         to stand for every srcu callback. 
> 
> I didn't need the callbacks to sleep too, I just needed the read-side
> srcu bit.
> 
> There's an argument against making the callbacks able to sleep like that
> in that you typically want to minimize the amount of work done in the
> callbacks, allowing them to sleep invites to callbacks that do _way_ too
> much work.
> 
> I haven't made my mind up if I care yet.. :-)

I prefer that they don't sleep.  Easy to push anything that needs to
sleep off to a work queue.  And allowing sleeping in an SRCU callback
function sounds like something that could cause serious problems down
the road.

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