From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 57D3EAAC for ; Thu, 16 Jul 2015 15:53:11 +0000 (UTC) Received: from relay4-d.mail.gandi.net (relay4-d.mail.gandi.net [217.70.183.196]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id BC2D7EB for ; Thu, 16 Jul 2015 15:53:10 +0000 (UTC) Date: Thu, 16 Jul 2015 08:53:02 -0700 From: Josh Triplett To: Kristen Accardi Message-ID: <20150716155302.GA2304@jtriplet-mobl1> References: <1489458.8WDRattPkl@vostro.rjw.lan> <1455994.zAMIqEIJx2@vostro.rjw.lan> <2869041.AWiygZspUy@vostro.rjw.lan> <20150716011056.GA8931@x> <1437038341.6856.22.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Cc: "Brown, Len" , "ksummit-discuss@lists.linuxfoundation.org" , Alan Stern , Kristen Carlson Accardi , Grant Likely Subject: Re: [Ksummit-discuss] [TECH TOPIC] System-wide interface to specify the level of PM tuning List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, Jul 16, 2015 at 03:44:57PM +0000, Kristen Accardi wrote: > On Thu, Jul 16, 2015 at 2:19 AM David Woodhouse wrote: > > > On Wed, 2015-07-15 at 18:10 -0700, Josh Triplett wrote: > > > > > > > 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. > > > > Not to the user, perhaps. But it's not *so* unreasonable to let each of > > the distros tune things for *their* class of users. We might want base > > profiles for 'server', 'desktop' and 'laptop on battery' that distros > > work from. > > > > > We need to be able to give even the distros more help than they have now. > The problem is that the distros simply don't have the knowledge to tune > *all* the knobs appropriately. If we gave them one knob as you suggested > (and what Rafael is suggesting) set to a sane default determined by the > kernel - they could then use whatever userspace tool to change it based on > whatever parameters they want. Even if there's a single knob, that *still* doesn't let us turn on power management features that break with certain devices. > But although that's complex, it's not the real problem. > > > > The real problem, as others have said, is when we have power management > > features which work fine for 99% of the population, but fail > > occasionally on broken hardware. > > > > We can't easily blacklist the known-broken devices or whitelist the > > good ones, and we end up having to turn the feature off by default. > > > > Sure, a DMI match on "HP" and "TO BE FILLED BY OEM" would often go a > > long way for a certain class of problem, but even that's not sufficient > > :) > > > > driver maintainers don't want to maintain blacklist/whitelist because it's > hard. It'd be nice to be able to load a black list or white list of > devices from the filesystem like we do with firmware. If the devices are identifiable from userspace, udev or similar could set these settings from a rules file. But the kernel already has quirk tables for various hardware, and that seems appropriate to continue putting in the kernel. - Josh Triplett