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

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Message-ID: <20180709144338.GS2476@hirez.programming.kicks-ass.net>
Date:   Mon, 9 Jul 2018 16:43:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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 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