From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [Query-CPUIdle]: Not much activity in C0 state Date: Tue, 03 Sep 2013 15:32:56 +0200 Message-ID: <5225E508.2060407@linaro.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Viresh Kumar Cc: "Rafael J. Wysocki" , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , Lists linaro-kernel , Suresh.Srinivasan@arm.com, Amit Kucheria , Sudeep KarkadaNagesha List-Id: linux-pm@vger.kernel.org On 08/27/2013 12:23 PM, Viresh Kumar wrote: > Hi Guys, >=20 > I was trying to run following on my thinkpad: >=20 > watch -n1 cat /sys/devices/system/cpu/cpu*/cpuidle/state*/usage >=20 > I can see lots of activities on State 1-4, but not much on state 0.. > I thought we should enter this state as soon as we come out to > non-idle state.. And so this count must be changing quite rapidly. >=20 > Is this a bug? Hi Viresh, the menu governor tries always to stick to C1 (state1) as default state= , look at the menu_select function. The state0 (not C0 but 'poll') will happen when the next timer event is less than 5us, this occurs rarely. You can easily spot it by doing while $(true); usleep 2; done The poll state is x86 specific where the cpu detects the 'rep nop' instructions to do some power saving. Hope that helps -- Daniel --=20 Linaro.org =E2=94=82 Open source software for= ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog