linux-kernel - Re: [RFC PATCH 11/15] x86: Nohz task support

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Message-ID: <20101221141950.GG1750@nowhere>
Date:	Tue, 21 Dec 2010 15:19:54 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	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 11/15] x86: Nohz task support

On Tue, Dec 21, 2010 at 09:05:29AM +0100, Peter Zijlstra wrote:
> On Tue, 2010-12-21 at 02:30 +0100, Frederic Weisbecker wrote:
> > On Mon, Dec 20, 2010 at 05:23:19PM +0100, Peter Zijlstra wrote:
> > > On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> > > > 
> > > > Implement the thread flag, syscalls and exception hooks for
> > > > nohz task support.
> > > > 
> > > 
> > > I saw:
> > >  - syscall
> > >  - do_int3
> > >  - do_debug (int1)
> > >  - #PF
> > > 
> > > So where's all other interrupts?
> > 
> > No need to handle them.
> > 
> > We have:
> > 
> > rcu_irq_enter() rcu_irq_exit() rcu_nmi_enter() rcu_nmi_exit()
> > and they already act as pauses into extended quiescent states, which
> > is enough for our needs.
> 
> Oh, and RCU is the only thing you need to worry about is it?

wrt userspace/kernelspace switches yes, for now. But perhaps I'll discover
more reasons to hook into that boundary.
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