From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH 1/3] PM / QoS: Make it possible to expose PM QoS latency constraints Date: Thu, 08 Mar 2012 15:18:31 -0800 Message-ID: <87zkbq8ywo.fsf@ti.com> References: <201203040101.53177.rjw@sisk.pl> <201203082227.50138.rjw@sisk.pl> <87haxyaguz.fsf@ti.com> <201203082337.23821.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from na3sys009aog133.obsmtp.com ([74.125.149.82]:57577 "EHLO psmtp.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756413Ab2CHXSb (ORCPT ); Thu, 8 Mar 2012 18:18:31 -0500 Received: by mail-iy0-f172.google.com with SMTP id z13so1504226iaz.31 for ; Thu, 08 Mar 2012 15:18:30 -0800 (PST) In-Reply-To: <201203082337.23821.rjw@sisk.pl> (Rafael J. Wysocki's message of "Thu, 8 Mar 2012 23:37:23 +0100") Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: "Rafael J. Wysocki" Cc: Linux PM list , Linux MMC list , Guennadi Liakhovetski , Chris Ball , Ulf Hansson , Magnus Damm , Linus Walleij , Adrian Hunter , Mark Brown "Rafael J. Wysocki" writes: > On Thursday, March 08, 2012, Kevin Hilman wrote: >> "Rafael J. Wysocki" writes: >> >> > On Thursday, March 08, 2012, Kevin Hilman wrote: >> >> "Rafael J. Wysocki" writes: >> >> >> >> > From: Rafael J. Wysocki >> >> > >> >> > A runtime suspend of a device (e.g. an MMC controller) belonging to >> >> > a power domain or, in a more complicated scenario, a runtime suspend >> >> > of another device in the same power domain, may cause power to be >> >> > removed from the entire domain. In that case, the amount of time >> >> > necessary to runtime-resume the given device (e.g. the MMC >> >> > controller) is often substantially greater than the time needed to >> >> > run its driver's runtime resume callback. That may hurt performance >> >> > in some situations, because user data may need to wait for the >> >> > device to become operational, so we should make it possible to >> >> > prevent that from happening. >> >> > >> >> > For this reason, introduce a new sysfs attribute for devices, >> >> > power/pm_qos_latency_us, allowing user space to specify the upper >> >> >> >> If we're expecting to have more of these knobs, maybe having a pm_qos >> >> subdir under power will keep down the clutter in /sys/devices/.../power. >> >> This knob would then be /sys/devices/.../power/pm_qos/pm_qos_latency_us. >> > >> > I'm not sure how difficult it is to create a subdir in sysfs under something >> > that is not a kobject. >> > >> > Besides, this follows the convention already used by wakeup and runtime PM >> > attributes that don't have their own subdirs (although there may be a number >> > of them in each category). >> >> OK >> >> >> I think 'latency' alone is a bit too vague (wakeup latency? interrupt >> >> latency? I think wakeup latency is clearer. Another possibility is >> >> resume latency, IMO, that will lead to confusion about whether this >> >> field also affects system suspend/resume. >> > >> > I think "wakeup latency" will lead to more confusion because of the >> > wakeup-related attributes. >> >> What confusion? All of those are related to device wakeups from some >> low power state, and so is this proposed latency attribute. So I don't >> understand the potential confusion. > > The word "wakeup" may refer to many different things, as well as the word > "resume". :-) Yes, but what's the confusion in this case? IMO, The existing /sys/devices/.../power/wakeup* meaning is the same meaning as as for the wakeup latency in this patch, so I don't understand where the confusion would be. Kevin