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 13:58:08 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	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>,
	Arjan Dan De Ven <arjan@...ux.intel.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

Thomas Gleixner <tglx@...utronix.de> writes:
>
> Vs. the interrupt/timer/other crap madness:
>
>  - We really don't want to have an interrupt balancer in the kernel
>    again, but we need a mechanism to prevent the user space balancer
>    trainwreck from ruining the power saving party.

Why not? I think the kernel is exactly the right place for it.
It's essentially a scheduling problem. Scheduling in user space
is not a good idea.

With MSI-X the drivers just want a static setting. User space
shouldn't mess with it. 

Some of the workarounds for user space messing with it (like that
interrupt rmap code) are really bad and just a workaround for doing the
scheduling in the wrong place.

For dynamic changes it should indeed by part of scheduling,
following similar rules, with only high level policy input
from userland.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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