linux-kernel - Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

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Message-ID: <563B6642.2090803@linux.intel.com>
Date:	Thu, 5 Nov 2015 06:22:58 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

On 11/5/2015 2:09 AM, Peter Zijlstra wrote:

> I can see such a scheme having a fairly big impact on latency, esp. with
> forced idleness such as this. That's not going to be popular for many
> workloads.

idle injection is a last ditch effort in thermal management, before
this gets used the hardware already has clamped you to a low frequency,
reduced memory speeds, probably dimmed your screen etc etc.

at this point there are 3 choices
1) Shut off the device
2) do uncoordinated idle injection for 40% of the time
3) do coordinated idle injection for 5% of the time

as much as force injecting idle in a synchronized way sucks, the alternatives are worse.


>

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