2008-02-21 07:02:53

by youquan_song

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@localhost ~]# 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.

2008-02-21 20:38:07

by Pallipadi, Venkatesh

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

>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of
>[email protected]
>Sent: Wednesday, February 20, 2008 11:01 PM
>To: [email protected]
>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@localhost ~]# 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