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

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Message-ID: <20111024120718.GD2273@linux.vnet.ibm.com>
Date:	Mon, 24 Oct 2011 05:07:18 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
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 Sun, Oct 16, 2011 at 06:49:15PM -0700, Josh Triplett wrote:
> 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.

I have added this to my todo list, but would welcome a patch.

							Thanx, Paul

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