linux-kernel - Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

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Date:	Tue, 05 Jun 2012 18:52:53 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Luck\\, Tony" <tony.luck@...el.com>,
	"Yu\\, Fenghua" <fenghua.yu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	"Siddha\\, Suresh B" <suresh.b.siddha@...el.com>,
	"Mallick\\, Asit K" <asit.k.mallick@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>, linux-pm <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or
 nmi

On 6/5/2012 4:13 PM, Andi Kleen wrote:
>> And aside of the above requirements it should add the ability to deal
>> with the fact that aside of server workloads this needs to be able to
>> cope with appplications in the embedded/mobile space which know more
>> about the future system state than the scheduler itself.
> 
> Well solving world hunger in one try is hard. Baby steps are easier.
> 
> What I think would be useful short term is a clean mechanism for drivers
> to lock a interrupt onto a CPU, without irqbalanced touching it. 
> This would be mainly for MSI-X drivers to spread their interrupts properly
> and give better performance out of the box.


like the IRQ_NO_BALANCING flag ? ;-)


> 
> Another short term case is the power aware interrupt routing now on recent 
> Intel CPUs.  In this case the interrupt needs logical focus to multiple CPUs 
> and the hardware makes the decision (essentially it does power aware load 
> balancing in hardware). Again nobody else should touch it.

PAIR is hard, it sadly needs a mostly complete revamp on how Linux does
interrupts. t

> 
> Then maybe this mechanism could be extended with a power aware 
> software solution with some input from the load balancer like you suggested. 

irqbalanced at least tries to be power aware.
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