Re: [Ksummit-discuss] [TECH TOPIC] System-wide interface to specify the level of PM tuning

[Josh Triplett <josh@joshtriplett.org>]

On Thu, Jul 16, 2015 at 12:44:01AM +0200, Rafael J. Wysocki wrote:
> On Tuesday, July 14, 2015 06:51:31 PM Daniel Vetter wrote:
> > On Tue, Jul 14, 2015 at 1:07 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> > > However, there are places in the kernel where there is a real tradeoff between
> > > power and performance (or power and capacity in general) and there are places
> > > that tend to keep conservative settings for fear of exposing latent bugs to
> > > a wide community of users.
> > >
> > > Those might benefit from allowing the users to relax the settings globally
> > > if they want to.
> > 
> > Well that's the approach I don't like personally. Essentially we
> > should be the experts on what works and what doesn't. But then kernel
> > developers chicken out and dump this problem onto users, which happily
> > enable all kinds of options they hear about. And then when it eats
> > their data or crashes machines everyone shrugs and says "oh well you
> > probably have one of the broken machines, don't enable this" and moves
> > on.
> > 
> > There's certainly the case that some tuning stuff in core kernel has
> > real downsides to either perf or power, but generally (for device
> > drivers) I feel like simply not enabling the all the power features is
> > a cheap way to chicken out of bugs reports and responsibility. I'm
> > somewhat opionated on this ;-)
> 
> But that's what's happening.  Many PM features are not enabled by default for
> this reason or another.
> 
> The point here is whether or not we want to have a way to make all of them be
> enabled by default instead and see what happens, for example.

To some degree that seems like an admission of defeat: we can't possibly
do the right thing by default, so we give up and add a way for the user
to configure it.

We should be selecting the most sensible combination of power and
performance by default; we should not punt that question to the average
user, *or* to the distros.

- Josh Triplett