Re: [PATCH v7 2/6] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

[Sudeep Holla]

On 04/07/16 14:17, Rafael J. Wysocki wrote:
> On Monday, July 04, 2016 02:00:03 PM Sudeep Holla wrote:
> > On 01/07/16 14:07, Daniel Lezcano wrote:
> > > On 06/28/2016 03:55 PM, Sudeep Holla wrote:
> > > > ACPI 6.0 introduced an optional object _LPI that provides an alternate
> > > > method to describe Low Power Idle states. 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.
> > > >
> > > > This patch adds initial support for Platform coordination scheme of LPI.
> > > >
> > > > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > > > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> > > > ---
> > >
> > > Hi Sudeep,
> > >
> > > I looked at the acpi processor idle code sometime ago and from my POV,
> > > it was awful, unnecessary complex and very difficult to maintain. The
> > > usage of flags all over the places is significant of the lack of control
> > > of the written code.
> >
> > So you have any specific things in mind ? That's too broad and I know
> > it's not so clean, but it's so for legacy reasons. I would leave that
> > to Rafael to decide as it takes lots of testing to clean up these code.
>
> The cleanup needs to be done at one point.
>
> Question is when to do it, before adding LPI support or after doing that
> (and each option has its pros and cons IMO).
>
> > > Even if you are not responsible of this implementation, the current
> > > situation forces you to add more awful code on top of that, which is
> > > clearly against "making Linux better".
> >
> > OK
>
> So if there are cases in which you need to make the code more complex
> because of the legacy stuff in there, I'd say it's better to clean it up
> first.

I am not sure if Daniel was referring to anything specific. I have
cleaned up in patch 1/6 for cstate. More cleanups can be done there but
needs better understanding and reasoning for the current code which I
don't have as they are mostly x86 related.

Unless someone points me what they would like to change and how, I don't
have much in my mind to do here. Yes it may not look as clean as other
code in the kernel relatively, but without complete understanding of the
history/reasoning for the current state of code I wouldn't touch
anything I don't understand.

I am open to make changes if there's something specific. Sorry I can't
go ahead making changes the way I think based on some vague idea that
the current code is not clean.

--
Regards,
Sudeep