linux-kernel - Re: [PATCH v9 0/7] ACPI / processor

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Date:	Thu, 14 Jul 2016 03:15:27 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	ACPI List <linux-acpi@...r.kernel.org>,
	Vikas Sajjan <vikas.cha.sajjan@....com>,
	Sunil <sunil.vl@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Prashanth Prakash <pprakash@...eaurora.org>,
	Al Stone <al.stone@...aro.org>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	ALKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v9 0/7] ACPI / processor_idle: Add ACPI v6.0 LPI support

On Tue, Jul 12, 2016 at 2:59 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>
>
> On 12/07/16 13:09, Rafael J. Wysocki wrote:
>>
>> On Tuesday, July 12, 2016 12:42:06 PM Sudeep Holla wrote:
>>>
>>>
>>> On 08/07/16 18:07, Sudeep Holla wrote:
>>>>
>>>> ACPI 6.0 introduced LPI(Low Power Idle) states that provides an
>>>> alternate
>>>> method to describe processor idle states. It extends the specification
>>>> to allow the expression of idle states like C-states selectable by the
>>>> OSPM when a processor goes idle, but may affect more than one processor,
>>>> and may affect other system components.
>>>>
>>>> LPI extensions leverages the processor container device(again introduced
>>>> in ACPI 6.0) allowing to express which parts of the system are affected
>>>> by a given LPI state. It defines the local power states for each node
>>>> in a hierarchical processor topology. The OSPM can use _LPI object to
>>>> select a local power state for each level of processor hierarchy in the
>>>> system. They used to produce a composite power state request that is
>>>> presented to the platform by the OSPM.
>>>>
>>>> Since multiple processors affect the idle state for any non-leaf
>>>> hierarchy
>>>> node, coordination of idle state requests between the processors is
>>>> required. ACPI supports two different coordination schemes: Platform
>>>> coordinated and  OS initiated.
>>>>
>>>
>>> I was hoping to get this in v4.8 now that merge window is
>>> delayed/extended if you have no further comments on this series.
>>
>>
>> I'll get to it in the next couple of days.  If it looks all good and there
>> are
>> no comments, I'll queue it up.
>>
>
> Thanks for the update.

I've just looked at patch [2/7] and there still are things I'm not
particularly liking in it.

Apart from a bunch of minor stuff, acpi_processor_get_lpi_info() is
not my favorite.  The way it creates all of those temporary data
structures and then walks them recursively seems a bit excessive.

I need to think about it a bit more, so I'll send my comments on that
patch later this week.

Thanks,
Rafael