linux-kernel - Re: [PATCH tip/core/rcu 31/86] rcu: further lower priority in rcu

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Message-ID: <1304328786.26772.8.camel@marge.simson.net>
Date:	Mon, 02 May 2011 11:33:06 +0200
From:	Mike Galbraith <efault@....de>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 31/86] rcu: further lower priority in
 rcu_yield()

On Mon, 2011-05-02 at 01:11 -0700, Paul E. McKenney wrote:
> On Sun, May 01, 2011 at 07:51:04PM +0200, Mike Galbraith wrote:
> > On Sun, 2011-05-01 at 06:21 -0700, Paul E. McKenney wrote:
> > > From: Paul E. McKenney <paul.mckenney@...aro.org>
> > > 
> > > Although rcu_yield() dropped from real-time to normal priority, there
> > > is always the possibility that the competing tasks have been niced.
> > > So nice to 19 in rcu_yield() to help ensure that other tasks have a
> > > better chance of running.
> > 
> > But.. that just prolongs the pain of overhead you _have_ to eat, no?  In
> > a brief surge, fine, you can spread the cost out.. but how do you know
> > when it's ok to yield?
> 
> I modeled this code on the existing code in ksoftirqd.  But yes, this is
> a heuristic.  I do believe that it is quite robust, but time will tell.

(It probably is fine, but when I see 'yield', alarms and sirens go off)

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