RE: [PATCHSET] 0/3 Dynamic cpufreq governor and updates to ACPI P-state driver

["Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>]

 
Hi,
 
I do not have any performance numbers taken from actual probes. 
We have seen in our testing that the the frequency does change based on
the cpu usage.
For example, on a Centrino system, 
- frequency will be lowest when system is idle 
- frequency will be somewhere in the mid-range when you run single app
like mp3/mpeg player
- frequency will be maximum when you run multiple apps 
And with the kind of power savings that comes with these frequency
changes, this behaviour 
results in  longer battery life. However, as yet I do not have any
numbers to quantify this gain, 
mainly because I do not have any setup where I can measure actual power.
 
Thanks,
-Venkatesh  
 

	-----Original Message-----
	From: Mukesh Rajan [mailto:megabyte1024@hotmail.com] 
	Sent: Tuesday, October 21, 2003 4:18 PM
	To: Pallipadi, Venkatesh
	Cc: cpufreq@www.linux.org.uk; linux-kernel@vger.kernel.org;
linux-acpilinux-acpi@intel.com
	Subject: [PATCHSET] 0/3 Dynamic cpufreq governor and updates to
ACPI P-state driver
	
	
	Hii,

	I was wondering if you had any numbers (physical measurements)
proving the same. Over an year ago, I had implemented the same idea on a
Compaq IPAQ (Strong ARM based running ARM Linux). I initially had to fix
the CPU freq code which was broken to get everything working right. But
after all the trouble, with actual probes (NI-DAQ board doing voltage
sampling et al) I measured very little savings in power at all. I
attributed those observations to questionable load average calculations
and very small power savings margin and simply moved on.

	~ Mukesh 

	(Please cc: as I am not in list)

	Hi,

	Most of the latest CPUs (laptop CPUs in particular) have feature


	which enable very low latency P-state transitions 

	(like Enhanced Speedstep Technology-EST). Using this feature, 

	we can have a lightweight in kernel cpufreq governor, 

	to vary CPU frequency depending on the CPU usage. The 

	advantage being low power consumption and also cooler laptops.

	Another related change is enhancing the current ACPI P-state 

	driver to handle:

	EST (and MSR based P-state transitions), make the driver SMP 

	aware and introduce HT coordination in the driver (HT siblings 

	share the same CPU frequency).

	The patches that follow this mail addresses the above issues. 

	They are against 2.6-test7 kernel. Many thanks to Dominik for 

	his comments and suggestions.

	The patches will work on all laptops with EST technology 

	(Centrino) and also on any other system that supports low 

	latency frequency change. 

	Reviews/testing of patches are most welcome.

	Thanks,

	-Venkatesh


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