linux-kernel - Re: Power Saving

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Message-ID: <20071120011236.GA17420@redhat.com>
Date:	Mon, 19 Nov 2007 20:12:36 -0500
From:	Dave Jones <davej@...hat.com>
To:	Stephen Clark <Stephen.Clark@...lark.us>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Power Saving

On Mon, Nov 19, 2007 at 08:05:29PM -0500, Stephen Clark wrote:
 
 > >I think by throttling, you actually mean changing frequency/voltage ?
 > >(throttling is something else, where the CPU skips every n cycles,
 > > which doesn't actually save any power)
 > >
 > well what about the info from /proc/
 > 
 > cat /proc/acpi/processor/CPU0/info
 > processor id:            0
 > acpi id:                 0
 > bus mastering control:   no
 > power management:        yes
 > throttling control:      yes
 > limit interface:         yes
 > 
 > and:
 > cat /proc/acpi/processor/CPU0/throttling
 > state count:             2
 > active state:            T0
 > states:
 >    *T0:                  00%
 >     T1:                  50%

See above. These are throttling states, used typically
if the system is overheating.

 > [root@...er ~]# cat /proc/acpi/processor/CPU0/power
 > active state:            C2
 > max_cstate:              C8
 > bus master activity:     d18324c9
 > states:
 >     C1:                  type[C1] promotion[C2] demotion[--] 
 > latency[000] usage[01340140]
 >    *C2:                  type[C2] promotion[--] demotion[C1] 
 > latency[090] usage[02980043]
 > 
 > ????

C states are unrelated to frequency/voltage scaling (which are P states)
They get taken advantage of automatically by ACPI as you can
see from the usage fields.

	Dave

-- 
http://www.codemonkey.org.uk
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