Re: thermal: uevent/netlink with step_wise?

[Brian Norris <computersforpeace@gmail.com>]

Hi Durga,

On Thu, Apr 02, 2015 at 04:28:16AM +0000, R, Durgadoss wrote:
> >-----Original Message-----
> >From: Brian Norris [mailto:computersforpeace@gmail.com]
> >Sent: Thursday, April 2, 2015 2:47 AM
> >To: linux-pm@vger.kernel.org
> >Cc: R, Durgadoss; Brown, Len; Lukasz Majewski; Eduardo Valentin
> >Subject: Re: thermal: uevent/netlink with step_wise?
> >
> >On Tue, Mar 31, 2015 at 03:43:48PM -0700, Brian Norris wrote:
> >> Particularly, I'm looking right now at using the uevent/netlink
> >> notification mechanism. It seems that this is only active when we use
> >> the 'user_space' governor, meaning I can't get any user-space
> >> notifications when using the in-kernel governor. Am I missing something,
> >> or is this a known limitation? Is there any reason we can't enable both?
> 
> When we use an in-kernel governor, we expect that the governor takes care of 
> all the required throttling etc. Hence, we did not add notification for
> in-kernel governors.
> 
> And we let the user space decide the actions when user space governor
> is selected and this requires notification.

OK, thanks for the explanation. I guess that matches my reading of the
code.

> That said,
> I do not think we have a hard rule saying we should not notify
> User space in in kernel governors. I think you can add it in your
> driver if you need it..

OK. I suppose I may do that if I decide I need that. But if I'm going to
be doing other general thermal management aspects from user space, I may
just defer entirely to user-space instead, and ignore the in-kernel
governor. I'm now trying to determine if there are many (any?) downsides
to that.

> >> For the user-space side, I'd mostly be interested in being a consumer;
> >> e.g., display warnings in high-temperature scenarios; although I might
> >> also use it to trigger some user-space cooling mechanisms.
> >
> >I'm noticing two additional interesting details.
> >
> >1. There's a separate netlink event mechanism that has never been used.
> >See generate_netlink_event(), from this commit:
> >
> >commit 4cb18728709683c91a5f6f8d5f337bfb498b089a
> >Author: R.Durgadoss <durgadoss.r@intel.com>
> >Date:   Wed Oct 27 03:33:29 2010 +0530
> >
> >    thermal: Add event notification to thermal framework
> 
> This netlink notification was added much before we had the
> UEvent reporting.

Right, it looked that way.

> Once we had UEvent reporting, We even
> discussed about removing this one. Afraid of breaking any
> user space depending on this, we have not done that.

But no one calls this function, so how would it break user space? Or is
Intel maintaining a body of out-of-tree code that uses this?

Thanks for your comments.

Brian