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 21:49:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"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

On Tue, 2012-06-05 at 21:43 +0200, Thomas Gleixner wrote:
> 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.

What's wrong with having an interrupt balancer tied to the scheduler
which optimistically tries to avoid interrupting nohz/isolated/idle
cpus?

>  - The timer issue is mostly solved by the existing nohz stuff
>    (plus/minus the few bugs in there).

Its not.. if you create an isolated domain there's no way to expel
existing timers from there.

>  - The other details (silly IPIs) and cross CPU timer arming) are way
>    easier to solve by a proper prohibitive state than by chasing that
>    nonsense all over the tree forever. 

But we need to solve all that without a prohibitibe state anyway for the
isolation stuff to be useful.


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