linux-kernel - Re: [RFC PATCH 00/15] Nohz task support

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Message-ID: <4D10B214.8010305@redhat.com>
Date:	Tue, 21 Dec 2010 15:56:36 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	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 00/15] Nohz task support

On 12/21/2010 01:33 AM, Frederic Weisbecker wrote:
> On Mon, Dec 20, 2010 at 10:44:46AM -0500, Steven Rostedt wrote:
> >  On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> >  >  The timer interrupt handles several things like preemption,
> >  >  timekeeping, rcu, etc...
> >  >
> >  >  However it appears that sometimes it is simply useless like
> >  >  when a task runs alone and even more when it is in userspace
> >  >  as RCU doesn't need it at all in such case.
> >  >
> >  >  It appears that HPC workload would get some win of such timer
> >  >  deactivation, and perhaps also the Real Time world as this
> >  >  minimizes the critical sections due to way less interrupts to
> >  >  handle.
> >  >
> >  >  It works through the procfs interface:
> >  >
> >  >  echo 1>  /proc/self/nohz
> >
> >  I wounder if we could just have this happen automatically.
>
> But this would add some global overhead, especially in the syscall
> path as we need to take the slow path to hook userspace resume/exit.

This is zero as there is already a test on thread_info->flags on the 
syscall exit path.

(or I misunderstood you - what's the purpose of the slow path?)

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

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