linux-kernel - Re: [RFC 0/3] Experimental patchset for CPPC

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Message-ID: <20140814205143.GY6758@twins.programming.kicks-ass.net>
Date:	Thu, 14 Aug 2014 22:51:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
Cc:	linux-kernel@...r.kernel.org, catalin.marinas@....com,
	mike.turquette@...aro.org, morten.rasmussen@....com,
	arjan@...ux.intel.com, mingo@...nel.org, len.brown@...el.com,
	rjw@...ysocki.net, linaro-acpi@...ts.linaro.org, arnd@...db.de,
	linux-acpi@...r.kernel.org, cpufreq@...r.kernel.org,
	patches@...aro.org
Subject: Re: [RFC 0/3] Experimental patchset for CPPC

On Thu, Aug 14, 2014 at 03:57:07PM -0400, Ashwin Chaugule wrote:
> 
> 
> What is CPPC:
> =============
> 
> CPPC is the new interface for CPU performance control between the OS and the
> platform defined in ACPI 5.0+. The interface is built on an abstract
> representation of CPU performance rather than raw frequency.  Basic operation
> consists of:

Why do we want this? Typically we've ignored ACPI and gone straight to
MSR access, intel_pstate and intel_idle were created especially to avoid
ACPI, so why return to it.

Also, the whole interface sounds like trainwreck (one would not expect
anything else from ACPI).

So _why_?

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