linux-kernel - Re: [RFC] Make need_resched() return true when rcu_urgent

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Message-Id: <20180709145440.GR3593@linux.vnet.ibm.com>
Date:   Mon, 9 Jul 2018 07:54:40 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Woodhouse <dwmw2@...radead.org>, mhillenb@...zon.de,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs
 requested

On Mon, Jul 09, 2018 at 04:43:38PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 09, 2018 at 07:29:32AM -0700, Paul E. McKenney wrote:
> 
> > OK, so here are our options:
> > 
> > 1.	Add the RCU conditional to need_resched(), as David suggests.
> > 	Peter has concerns about overhead.
> 
> Not only overhead, its plain broken, because:
> 
>  1) we keep preemption state in other places too
>  2) we check need_resched() in asm

Fair points.  And yes, the various asm checks and transitions have
made their presence known to me in other contexts of late.  :-/

So what would you suggest?

							Thanx, Paul