From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933385Ab0ECQmy (ORCPT ); Mon, 3 May 2010 12:42:54 -0400 Received: from tex.lwn.net ([70.33.254.29]:41285 "EHLO vena.lwn.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933161Ab0ECQmx (ORCPT ); Mon, 3 May 2010 12:42:53 -0400 Date: Mon, 3 May 2010 10:42:50 -0600 From: Jonathan Corbet To: Kevin Hilman Cc: mgross@linux.intel.com, aili@codeaurora.org, dwalker@codeaurora.org, tiwai@suse.de, bruce.w.allan@intel.com, davidb@quicinc.com, mcgrof@gmail.com, pavel@ucw.cz, linux-pm , lkml Subject: Re: [PATCH]PM QOS refresh against next-20100430 Message-ID: <20100503104250.7605d2bc@bike.lwn.net> In-Reply-To: <87y6g1547o.fsf@deeprootsystems.com> References: <20100430212043.GA30315@linux.intel.com> <20100503103300.6330e522@bike.lwn.net> <87y6g1547o.fsf@deeprootsystems.com> Organization: LWN.net X-Mailer: Claws Mail 3.7.5 (GTK+ 2.20.0; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 03 May 2010 09:40:11 -0700 Kevin Hilman wrote: > > One question, though... one clear use of this API is for drivers to > > say "don't go into C3 or deeper because things go wrong"; I'm about to > > add another one of those. It works, but the use of a > > PM_QOS_CPU_DMA_LATENCY requirement with a hard-coded number that one > > hopes is small enough seems a bit...indirect. I wonder if it would be > > clearer and more robust to add a new requirement^Wrequest type saying > > "the quality of service I need is shallow sleeps only"? > > The problem with that is portability. > > What does "shallow" mean? Well, shallow could mean that the state lacks the CPUIDLE_FLAG_DEEP flag; that should be relatively portable. In any case, it seems more so than "if I put in a 55us latency requirement, I'll stay out of C3". Just a thought, anyway; it's not like I've really worked through a plausible alternative API. jon