linux-kernel - RE: kernel-2.6.25-rc2, CPU C state "active state" always remain C0 unchangeable by cat 'proc/'

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Date:	Thu, 21 Feb 2008 12:24:23 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	<youquan_song@...ux.intel.com>, <linux-kernel@...r.kernel.org>
Cc:	"Song, Youquan" <youquan.song@...el.com>
Subject: RE: kernel-2.6.25-rc2,      CPU C state "active state" always remain C0 unchangeable by cat      'proc/'


>-----Original Message-----
>From: linux-kernel-owner@...r.kernel.org 
>[mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of 
>youquan_song@...ux.intel.com
>Sent: Wednesday, February 20, 2008 11:01 PM
>To: linux-kernel@...r.kernel.org
>Cc: Song, Youquan
>Subject: kernel-2.6.25-rc2, CPU C state "active state" always 
>remain C0 unchangeable by cat 'proc/'
>
>On Fedora9 Alpha with  kernel-2.6.25-rc2,
>I run " watch -n 0.1 "cat /proc/acpi/processor/CPU*/power | 
>grep 'active
>state'" ", I find that the CPU C state information "active 
>state" remain
>at "C0" and it do not change any time. The same issue also exit on
>2.6.24-rc2 kernel.
>But with RHEL5.1 kernel-2.6.18 the CPU C state information is normal.
>
>
>Every 0.1s: cat /proc/acpi/processor/CPU*/power | grep 'active 
>state'     
>                                                               
>         
>Thu Feb 21 09:44:33 2008
>
>active state:            C0
>active state:            C0
>active state:            C0
>active state:            C0
>active state:            C0
>active state:            C0
>active state:            C0
>active state:            C0
>
>On RHEL5.1  kernel-2.6.18-53.el5
>[root@...alhost ~]# cat /proc/acpi/processor/CPU*/power | grep 
>'active state'
>active state:            C2
>active state:            C2
>active state:            C2
>active state:            C2
>active state:            C2
>active state:            C3
>active state:            C2
>active state:            C3
>
>The hardware platform: bensley and santarosa.
>

I am not sure active state gives a lot of information about C-state. And
I really hate to see code waking up every .1 sec to check the active
state :-).
/proc/acpi/processor/*/power is marked deprecated upstream and if you
really want this field, you will have to disable CONFIG_CPU_IDLE in
upstream kernel. With CPU_IDLE you will get more detailed information
about all C-states entry counts and residencies under
/sys/devices/system/cpu/cpu*/cpuidle/

Thanks,
Venki
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