linux-kernel - Re: [Query-CPUIdle]: Not much activity in C0 state

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <5225E508.2060407@linaro.org>
Date:	Tue, 03 Sep 2013 15:32:56 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Suresh.Srinivasan@....com,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
Subject: Re: [Query-CPUIdle]: Not much activity in C0 state

On 08/27/2013 12:23 PM, Viresh Kumar wrote:
> Hi Guys,
> 
> I was trying to run following on my thinkpad:
> 
> watch -n1 cat /sys/devices/system/cpu/cpu*/cpuidle/state*/usage
> 
> 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.
> 
> 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



-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/