linux-kernel - Re: [PATCH] Extend mwait idle to optimize away CAL and RES interrupts to an idle CPU -v1

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Message-ID: <20120227095100.GC1112@zhy>
Date:	Mon, 27 Feb 2012 17:51:00 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Venki Pallipadi <venki@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Aaron Durbin <adurbin@...gle.com>,
	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Extend mwait idle to optimize away CAL and RES
 interrupts to an idle CPU -v1

On Mon, Feb 27, 2012 at 10:30:58AM +0100, Peter Zijlstra wrote:
> On Mon, 2012-02-27 at 17:08 +0800, Yong Zhang wrote:
> > On Mon, Feb 27, 2012 at 09:38:01AM +0100, Peter Zijlstra wrote:
> > > On Fri, 2012-02-24 at 14:13 +0800, Yong Zhang wrote:
> > > 
> > > > This remind me that we should have moved the irq_enter()/irq_exit() to
> > > > each arch's related irq handler.
> > > > see: http://marc.info/?l=linux-kernel&m=130709505700821&w=2
> > > > 
> > > > So Peter, is there someone alread on it? or it still worth doing now?
> > > 
> > > trouble was that some people didn't feel comfortable adding that
> > > overhead to plain resched IPIs that didn't need to do anything.
> > 
> > Any ideas on where the plain resched IPIs come from?
> 
> remote wakeups that don't queue I guess. 
> 
> IIRC I looked at it a while back and while not in the majority there
> were still a few (I only added counters, didn't look where they came
> from).
> 
> However since 518cd623 there'd be a lot more I guess..
> 
> Feel free to investigate. Also, some non-sched users of the resched ipi
> exist, eg. KVM uses it to kick a remote vcpu out from guest mode.

Thanks for the detail.

Will try to find if there is something interesting.

Thanks,
Yong
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