linux-kernel - Re: [PATCH tip/core/rcu 36/55] rcu: Prevent early boot set_need_resched() from __rcu

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Date:	Sun, 16 Oct 2011 18:49:15 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <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, 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 36/55] rcu: Prevent early boot
 set_need_resched() from __rcu_pending()

On Tue, Sep 06, 2011 at 11:00:30AM -0700, Paul E. McKenney wrote:
> From: Paul E. McKenney <paul.mckenney@...aro.org>
> 
> There isn't a whole lot of point in poking the scheduler before there
> are other tasks to switch to.  This commit therefore adds a check
> for rcu_scheduler_fully_active in __rcu_pending() to suppress any
> pre-scheduler calls to set_need_resched().  The downside of this approach
> is additional runtime overhead in a reasonably hot code path.

If you're concerned about the runtime overhead, this does seem like a
perfect candidate for jump labels.

- Josh Triplett
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