Re: [RFC PATCH 0/3] CFS idle injection

From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Eduardo Valentin <edubezval@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Arjan van de Ven <arjan@linux.intel.com>,
	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 0/3] CFS idle injection
Date: Fri, 6 Nov 2015 21:55:49 +0000	[thread overview]
Message-ID: <563D21E5.4050408@arm.com> (raw)
In-Reply-To: <20151106111030.6cc5a032@icelake>

On 11/06/2015 07:10 PM, Jacob Pan wrote:
> On Fri, 6 Nov 2015 18:30:01 +0000
> Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
>> On 05/11/15 10:12, Peter Zijlstra wrote:
>>>
>>> People, trim your emails!
>>>
>>> On Wed, Nov 04, 2015 at 08:58:30AM -0800, Jacob Pan wrote:
>>>
>>>>> I also like #2 too. Specially now that it is not limited to a
>>>>> specific platform. One question though, could you still keep the
>>>>> cooling device support of it? In some systems, it might make
>>>>> sense to enable / disable idle injections based on temperature.
>>>
>>>> One of the key difference between 1 and 2 is that #2 is open loop
>>>> control, since we don't have CPU c-states info baked into
>>>> scheduler.
>>>
>>> _yet_, there's people working on that. The whole power aware
>>> scheduling stuff needs that.
>>
>> Isn't the idle state information (rq->idle_state) already used in
>> find_idlest_cpu()?
>>
>> What we use in energy aware scheduling is quite similar but since
>> we're interested in the index information of the c-state (to access
>> the right element of the idle_state vectors of the energy model, we
>> added rq->idle_state_idx.
>>
> what i am interested is not per cpu idle state but rather at the package
> level or domain. It must be an indication for the overlapped idle time.
> Usually has to come from HW counters.

I see. We have a similar problem with the Energy Model (EM) on cluster 
level (sched domain level DIE). We iterate over the cpus of a sched 
group and declare the shallowest cpu idle state as the cluster idle 
state to index our EM. On a typical ARM system we have (active, WFI, 
cpu-off and cluster-off). But I guess for you the idle state index is 
only for core idle states and you can't draw any conclusions from this 
for the package idle states.