linux-kernel - Re: RFC: THE OFFLINE SCHEDULER

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Message-ID: <4A971C18.7050109@nortel.com>
Date:	Thu, 27 Aug 2009 17:51:52 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	raz ben yehuda <raziebe@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
	peterz@...radead.org, maximlevitsky@...il.com, efault@....de,
	riel@...hat.com, wiseman@...s.biu.ac.il,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: RFC: THE OFFLINE SCHEDULER

On 08/27/2009 03:09 PM, Thomas Gleixner wrote:

> That's just the wrong approach. All you need is a way to tell the
> kernel that CPUx can switch off the scheduler tick when only one
> thread is running and that very thread is running in user space. Once
> another thread arrives on that CPU or the single thread enters the
> kernel for a blocking syscall the scheduler tick has to be
> restarted.

That's an elegant approach...I like it.

How would you deal with per-cpu kernel threads (softirqs, etc.) or
softirq processing while in the kernel?  Switching off the timer tick
isn't sufficient because the scheduler will be triggered on the way back
to userspace in a syscall.

Chris
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