linux-kernel - Re: [RFC PATCH 15/15] nohz

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Message-ID: <4D10B2E9.9040806@redhat.com>
Date:	Tue, 21 Dec 2010 16:00:09 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 15/15] nohz_task: Procfs interface

On 12/21/2010 10:14 AM, Peter Zijlstra wrote:
> On Tue, 2010-12-21 at 02:24 +0100, Frederic Weisbecker wrote:
> >
> >  >  Also, I'm not quite happy with the pure userspace restriction, but at
> >  >  least I see why you did that event though you didn't mention that.
> >
> >  What do you mean? The fact that kernel threads can not be nohz task?
>
> No, that you key off kernel/user boundary transitions. Arguably one
> could allow simply system calls and page-faults to happen without
> restarting the tick, then again, RCU is very pervasive these days so I'm
> not quite sure you can actually make that happen.
>

For an example of a per-cpu flag that is checked on every exit with zero 
additional overhead on the flag clear case, look at TIF_USER_RETURN_NOTIFY.

-- 
error compiling committee.c: too many arguments to function

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