linux-kernel - Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle implementations

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Message-ID: <20131120140821.1d5607c2@ultegra>
Date:	Wed, 20 Nov 2013 14:08:21 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>, lenb@...nel.org,
	rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	Chris Leech <christopher.leech@...el.com>,
	David Miller <davem@...emloft.net>, rui.zhang@...el.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle
 implementations

On Wed, 20 Nov 2013 20:38:03 +0100 (CET)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Wed, 20 Nov 2013, Arjan van de Ven wrote:
> > 
> > but for powerclamp to work, it needs to inject a deep idle....  I'm
> > very ok using generic abstractions for that, but the abstraction
> > needs to then include a "don't be nice about picking shallow C
> > states for performance reasons, just pick something very deep"
> > parameter.
> 
> And that's what you should have done in the first place. Make the
> generic code take a parameter to indicate that. Or tell the scheduler
> to throttle the machine and go deep idle. That would also be helpful
> to others who might need some similar thing.
> 
I thought about that. Since the generic code is in performance critical
path and idle injection is a rare case. Then the question is do we
want sacrifice the 99% for %1 usage?

> No, you went with the worst design:
> 
>     - Hack it into some random driver
>     - Export random core interfaces so it's harder to change them
>     - Let others deal with the fallout
> 
> I'm cleaning up that kind of mess for more than 9 years now and I'm
> really disappointed that you went over to the "who cares, works for
> me" camp.
> 
> I can lively remember our discussions when we were cleaning up the
> whole timer mess together in order to make NOHZ actually useful. Your
> cursing about such code was definitely impressive back then.
> 
> Thanks,
> 
> 	tglx
> 
> 
> 
> 

[Jacob Pan]
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