From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from co9outboundpool.messaging.microsoft.com (co9ehsobe002.messaging.microsoft.com [207.46.163.25]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "Microsoft Secure Server Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 87D152C02A7 for ; Tue, 5 Feb 2013 07:02:48 +1100 (EST) Date: Mon, 4 Feb 2013 14:02:35 -0600 From: Scott Wood Subject: Re: Why is the e500v2 core not using cpuidle? To: Thomas Waldecker In-Reply-To: (from Thomas.Waldecker@tqs.de on Sat Feb 2 03:41:27 2013) Message-ID: <1360008155.14901.4@snotra> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; delsp=Yes; format=Flowed Cc: "Linux PPC dev mailing list \(linuxppc-dev@lists.ozlabs.org\)" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 02/02/2013 03:41:27 AM, Thomas Waldecker wrote: > Hi Scott, >=20 > >> Why is there no support for the cpuidle framework? > > Because nobody implemented it. :-) > That's the reason I thought before :-) >=20 > > The only reason I can think of to implement it on this chip would =20 > be to > > dynamically choose when to enter nap versus doze, rather than always > > just using doze. It's not clear whether the difference in power > > savings is worth it -- do you have any way of measuring? >=20 > Is the e500 only using doze? There are comments in the file > arch/powerpc/kernel/idle_e500.S > which are stating: > /* Go to NAP or DOZE now */ > or > /* Return from NAP/DOZE ...*/ >=20 > and because of this comments I thought that both modes are in use. e500 can use nap instead, but it's statically chosen via sysctl. The =20 default is doze. Entering nap requires flushing the cache, so you'd =20 only use nap if you care more about lowering idle power consumption =20 than performance, and you wake infrequently enough that you're not =20 burning more power on the cache flushes than you save with the deeper =20 idle state. > I have a way of measuring the power and it is also a small part of my =20 > masterthesis, > but it is not very meaningful because at the measuring point there =20 > are other peripheral > components too. >=20 > According to the comments can I activate the nap mode somehow? echo 1 > /proc/sys/kernel/powersave-nap If you're able to measure a meaningful difference between the two, I'd =20 be interested in hearing your results. > >> How can I debug the e500 idle modes? > >> Are there any statistics? > > Top reports idle percentage... > If the e500 and e500v2 are indeed using only the doze mode it > would be enough statistics. Whichever mode you have selected, that will be used for all idling. =20 Statistics would only be useful if the idle mode were dynamically =20 chosen. > Such statistics would be great for the doze, nap (and sleep for the =20 > whole package). The only way you'll get into sleep mode is through /sys/power/state. -Scott=