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 646CDAC2 for ; Thu, 16 Jul 2015 01:11:05 +0000 (UTC) Received: from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net [217.70.183.195]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id B1F9B17E for ; Thu, 16 Jul 2015 01:11:04 +0000 (UTC) Date: Wed, 15 Jul 2015 18:10:56 -0700 From: Josh Triplett To: "Rafael J. Wysocki" Message-ID: <20150716011056.GA8931@x> References: <1489458.8WDRattPkl@vostro.rjw.lan> <1455994.zAMIqEIJx2@vostro.rjw.lan> <2869041.AWiygZspUy@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2869041.AWiygZspUy@vostro.rjw.lan> 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 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 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