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

From: Arjan van de Ven <arjan@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>, Paul Turner <pjt@google.com>,
	Len Brown <len.brown@intel.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Rafael Wysocki <rafael.j.wysocki@intel.com>
Subject: Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection
Date: Thu, 5 Nov 2015 06:22:58 -0800	[thread overview]
Message-ID: <563B6642.2090803@linux.intel.com> (raw)
In-Reply-To: <20151105100922.GA3604@twins.programming.kicks-ass.net>

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.

>