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

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Date:	Wed, 4 Nov 2015 10:43:50 -0800
From:	Eduardo Valentin <edubezval@...il.com>
To:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.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 0/3] CFS idle injection

Hello Jacob, Srinivas,

On Wed, Nov 04, 2015 at 09:05:52AM -0800, Srinivas Pandruvada wrote:
> On Wed, 2015-11-04 at 08:58 -0800, Jacob Pan wrote:

<cut>
> > > > I have two choices for this code:
> > > > 1) be part of existing powerclamp driver but require exporting some
> > > >    sched APIs.
> > > > 2) be part of sched since the genernal rule applies when it comes
> > > > down to sycnhronized idle time for best power savings.
> > > > 
> > > > The patches below are for #2. There is a known problem with LOW RES
> > > > timer mode that I am working on. But I am hoping to get review
> > > > earlier.
> > > > 
> > > 
> > > 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. To
> > close the loop, perhaps we can export some internal APIs to the thermal
> > subsystem then the thermal governors can pick the condition to inject
> > idle.


Jacob,

I also like this direction. Having the proper APIs exported, creating a
cooling device that use them would be  natural path. Then, one could
create a thermal zone plugging a governor and the idle injection cooling
device that uses the exported APIs.

> > > Was there any particular reason you dropped the cooling device
> > > support?
> > > 
> > I did sysctl instead of thermal sysfs to conform the rest of the sched
> > tuning knobs. We could also have a proxy cooling device to call
> > internal APIs mentioned above.

Agreed here then.


> I think we should have cooling device as we are already using this
> cooling device. Once it pass RFC stage,I think we should consider add
> this.

Srinivas, 
Yes, that seens to be a good path to follow. Thanks.


> Thanks,
> Srinivas
> > 
> > Another reason is that, I intend to extend beyond thermal. Where we can
> > consolidate/sync idle work in semi-active and balanced workload.

I see. 

BR,

Eduardo Valentin
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