From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757207Ab0EDHx1 (ORCPT ); Tue, 4 May 2010 03:53:27 -0400 Received: from ksp.mff.cuni.cz ([195.113.26.206]:45184 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757201Ab0EDHx0 (ORCPT ); Tue, 4 May 2010 03:53:26 -0400 Date: Tue, 4 May 2010 06:16:37 +0200 From: Pavel Machek To: Jonathan Corbet Cc: Kevin Hilman , mgross@linux.intel.com, aili@codeaurora.org, dwalker@codeaurora.org, tiwai@suse.de, bruce.w.allan@intel.com, davidb@quicinc.com, mcgrof@gmail.com, linux-pm , lkml Subject: Re: [PATCH]PM QOS refresh against next-20100430 Message-ID: <20100504041637.GC5326@ucw.cz> References: <20100430212043.GA30315@linux.intel.com> <20100503103300.6330e522@bike.lwn.net> <87y6g1547o.fsf@deeprootsystems.com> <20100503104250.7605d2bc@bike.lwn.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100503104250.7605d2bc@bike.lwn.net> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 2010-05-03 10:42:50, Jonathan Corbet wrote: > 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". While C3 has maximum allowed latency (101usec, iirc), I believe there's no minimum, so someone could create platform with really quick C3 with perhaps only 10usec to enter... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html