linux-kernel - Re: [PATCH] CPU C-state breakage with PM Qos change

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Message-ID: <20120205035057.GA4948@gs62>
Date:	Sat, 4 Feb 2012 19:50:57 -0800
From:	mark gross <markgross@...gnar.org>
To:	"Pihet-XID, Jean" <j-pihet@...com>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	markgross <markgross@...gnar.org>, Kevin Hilman <khilman@...com>,
	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH] CPU C-state breakage with PM Qos change

On Fri, Feb 03, 2012 at 03:04:43PM +0100, Pihet-XID, Jean wrote:
> Looping in linux-pm
> 
> On Fri, Feb 3, 2012 at 1:14 AM, Venkatesh Pallipadi <venki@...gle.com> wrote:
> > Looks like change "PM QoS: Move and rename the implementation files"
> > made pm_qos depend on CONFIG_PM which depends on
> > PM_SLEEP || PM_RUNTIME
> >
> > That breaks CPU C-states with kernels not having these CONFIGs, causing CPUs
> > to spend time in Polling loop idle instead of going into deep C-states,
> > consuming way way more power. This is with either acpi idle or intel idle
> > enabled.
> >
> > Either CONFIG_PM should be enabled with any pm_qos users or
> > the !CONFIG_PM pm_qos_request() should return sane defaults not to break
> > the existing users. Here's is the patch for the latter option.
> I think the real question is whether PM QoS should be functional in
> all cases (as is ACPI) or whether only if certain options are set
> (CONFIG_PM).
> In the current code if CONFIG_PM is not enabled, a dummy PM QoS API is
> provided as function stubs in order for the build to succeed.
> 
> Rafael, Mark,
> What do you think? Should PM QoS be enabled in all cases? Are there
> any known dependencies with CONFIG_PM?

Yes I do think pm_qos interfaces should be enabled all the time and be
independent of CONFIG_PM.  Also, I still am not a fan of the renaming
patch but, as the argument for and against renaming cannot be based on
quantifiable things I've chosen not to let it bother me.

I think Venki's change is a band aid and we should fix it right by not
having a dependency on config_pm for the interface to behave.

I'll take a look at why there is now a dependency before I have more to
say.

--mark
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