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 8B5FFABF for ; Mon, 13 Jul 2015 22:40:29 +0000 (UTC) Received: from v094114.home.net.pl (v094114.home.net.pl [79.96.170.134]) by smtp1.linuxfoundation.org (Postfix) with SMTP id B74AAF1 for ; Mon, 13 Jul 2015 22:40:28 +0000 (UTC) From: "Rafael J. Wysocki" To: Daniel Vetter Date: Tue, 14 Jul 2015 01:07:04 +0200 Message-ID: <1455994.zAMIqEIJx2@vostro.rjw.lan> In-Reply-To: References: <1489458.8WDRattPkl@vostro.rjw.lan> <7hlheo9b7m.fsf@deeprootsystems.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" 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 Sunday, July 12, 2015 12:01:27 PM Daniel Vetter wrote: > On Fri, Jul 10, 2015 at 7:25 PM, Kevin Hilman wrote: > > "Rafael J. Wysocki" writes: > > > >> On Monday, July 06, 2015 01:49:45 PM Iyer, Sundar wrote: > > > > [...] > > > >>> Is a "single setting somewhere" even appropriate? It is actually the intelligence > >>> needed vs executing the actions? > >> > >> For one example, the default for most of the device/.../power/control files in > >> sysfs is "on" (meaning no runtime PM) while it might be "auto" (use runtime PM > >> if you can). Making that change for everybody in one go may lead to various > >> issues (that may be regarded as regressions then), but if we made it configurable, > >> people might choose to make that change for themselves if they wanted to. > > > > I'd be very supportive of some default knob (or cmdline option) to favor > > energy efficiency. For runtime PM, I suspect the resulting performance > > regressions are mostly (relatively) simple fixes, like enabling > > autosuspend, etc. > > > > Also, having a system-wide way to enable this mode would also enable us > > to find/report these bugs/regressions in a way that would be easily > > repeatable. With the current pile of knobs/tunables, it's often very > > hard to reproduce problems others may be seeing. > > My approach in drm/i915 is that there's just one default config and > that's the well-tuned one. Maybe gfx is special, but with todays > power-envelope constrained chips it's not a question of performance > _or_ power efficiency, but always _and_: Enabling power saving > features improves performance. 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. Thanks, Rafael