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

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Message-ID: <20131218155808.GG18464@localhost.localdomain>
Date:	Wed, 18 Dec 2013 16:58:10 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 04:11:58PM +0100, Peter Zijlstra wrote:
> 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.

Fair point!

Thanks.
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