linux-kernel - Re: [PATCH 05/13] rcu: Fix unraised IPI to timekeeping CPU

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Message-ID: <20131218151158.GV21999@twins.programming.kicks-ass.net>
Date:	Wed, 18 Dec 2013 16:11:58 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Stultz <john.stultz@...aro.org>,
	Alex Shi <alex.shi@...aro.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [PATCH 05/13] rcu: Fix unraised IPI to timekeeping CPU

On Wed, Dec 18, 2013 at 03:56:12PM +0100, Frederic Weisbecker wrote:
> Because scheduler_ipi() conditionally calls irq_enter() and irq_exit()
> (I wonder if that's a good idea btw, is that here to deal with spurious
> scheduler IPIs of some sort?)

No its because the traditional scheduler IPI did all the work from the
interrupt return path -- and like the comment in there says, for many of
the IPIs that's still true.

So going through the architectures and making all scheduler_ipi callers
do irq_enter/exit would actually make them slower.
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