The ondemand CPUFreq code -- I hope the functionality stays

The ondemand CPUFreq code -- I hope the functionality stays

[Miles Lane]

Hello,

It sounds, from comments in the discussion of CPU Hotplug locking
problems, as though you are considering deleting the ondemand CPUFreq
code.  If this happens, I hope that something that provides the same
functionality replaces it.  I really appreciate having my power
consumption automatically modulated on an as needed basis.  Power
management seems to be one of the areas where there is a lot of room
for improvement.

Thanks,
      Miles

Re: The ondemand CPUFreq code -- I hope the functionality stays

[Arjan van de Ven]

On Thu, 2006-07-27 at 10:54 +0200, Miles Lane wrote:
> Hello,
> 
> It sounds, from comments in the discussion of CPU Hotplug locking
> problems, as though you are considering deleting the ondemand CPUFreq
> code. 

Hi,

I think you misunderstood; we are considering removing the cpu hotplug
locking (from cpufreq), not ondemand itself. ondemand itself is not a
problem in itself, it's only the hotplug locking that's an issue (and
that issue is bigger than just ondemand btw)

Greetings,
   Arjan van de Ven
-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com

Re: The ondemand CPUFreq code -- I hope the functionality stays

[Patrick McFarland]

On Thursday 27 July 2006 04:54, Miles Lane wrote:
> Hello,
>
> It sounds, from comments in the discussion of CPU Hotplug locking
> problems, as though you are considering deleting the ondemand CPUFreq
> code.  If this happens, I hope that something that provides the same
> functionality replaces it.  I really appreciate having my power
> consumption automatically modulated on an as needed basis.  Power
> management seems to be one of the areas where there is a lot of room
> for improvement.

I think you've gotten confused. Ondemand is a horrible governor that only 
flips between two cpu frequencies, the lowest and the highest. Use the 
Conservative governor instead.

Also, the locking issues have nothing to do with Ondemand, its just that 
Ondemand's suckyness came up in the thread.

> Thanks,
>       Miles

-- 
Patrick McFarland || www.AdTerrasPerAspera.com
"Computer games don't affect kids; I mean if Pac-Man affected us as kids,
we'd all be running around in darkened rooms, munching magic pills and
listening to repetitive electronic music." -- Kristian Wilson, Nintendo,
Inc, 1989

Re: The ondemand CPUFreq code -- I hope the functionality stays

[Dave Jones]

On Thu, Jul 27, 2006 at 09:04:23PM -0400, Patrick McFarland wrote:

 > I think you've gotten confused. Ondemand is a horrible governor that only 
 > flips between two cpu frequencies, the lowest and the highest.

That isn't true.  I just double checked, and saw my core-duo changing
between all 4 states it offers.

 > Use the Conservative governor instead.

This governor is based on the same code as on-demand with some subtle
tweaks to make it not change the frequency as often.  If anything *this*
one should be less 'active' for you than ondemand.

What driver are you using ?

		Dave

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

Re: The ondemand CPUFreq code -- I hope the functionality stays

[Patrick McFarland]

On Thursday 27 July 2006 21:10, Dave Jones wrote:
> On Thu, Jul 27, 2006 at 09:04:23PM -0400, Patrick McFarland wrote:
>  > I think you've gotten confused. Ondemand is a horrible governor that
>  > only flips between two cpu frequencies, the lowest and the highest.
>
> That isn't true.  I just double checked, and saw my core-duo changing
> between all 4 states it offers.

This may have been fixed then.

>  > Use the Conservative governor instead.
>
> This governor is based on the same code as on-demand with some subtle
> tweaks to make it not change the frequency as often.  If anything *this*
> one should be less 'active' for you than ondemand.

This used to be not true at all. Go back in the LKML archives about a year or 
so.

> What driver are you using ?

K7.

> 		Dave

-- 
Patrick McFarland || www.AdTerrasPerAspera.com
"Computer games don't affect kids; I mean if Pac-Man affected us as kids,
we'd all be running around in darkened rooms, munching magic pills and
listening to repetitive electronic music." -- Kristian Wilson, Nintendo,
Inc, 1989

Re: The ondemand CPUFreq code -- I hope the functionality stays

[Miles Lane]

On 7/28/06, Dave Jones <davej@redhat.com> wrote:
> On Thu, Jul 27, 2006 at 09:04:23PM -0400, Patrick McFarland wrote:
>
>  > I think you've gotten confused. Ondemand is a horrible governor that only
>  > flips between two cpu frequencies, the lowest and the highest.
>
> That isn't true.  I just double checked, and saw my core-duo changing
> between all 4 states it offers.

Yep, the ondemand governor switches between all frequencies on my
Pentium 4 M laptop.  It's a HP Pavillion dv1240us.

>  > Use the Conservative governor instead.
>
> This governor is based on the same code as on-demand with some subtle
> tweaks to make it not change the frequency as often.  If anything *this*
> one should be less 'active' for you than ondemand.

I have tried the other governers (albeit a while ago) and found they
didn't manage power anywhere near as well as ondemand.  Perhaps
results vary for each governor according to CPU and chipset.

      Miles

Re: The ondemand CPUFreq code -- I hope the functionality stays

[Thomas Tuttle]

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On July 27 at 21:04 EDT, Patrick McFarland hastily scribbled:
> On Thursday 27 July 2006 04:54, Miles Lane wrote:
> > Hello,
> >
> > It sounds, from comments in the discussion of CPU Hotplug locking
> > problems, as though you are considering deleting the ondemand CPUFreq
> > code.  If this happens, I hope that something that provides the same
> > functionality replaces it.  I really appreciate having my power
> > consumption automatically modulated on an as needed basis.  Power
> > management seems to be one of the areas where there is a lot of room
> > for improvement.
> 
> I think you've gotten confused. Ondemand is a horrible governor that only 
> flips between two cpu frequencies, the lowest and the highest. Use the 
> Conservative governor instead.

AFAIK, ondemand implements the following.

Many times per second, do the following:
	Calculate CPU usage since last check.
	If CPU usage > high threshold, set frequency to maximum.
	If CPU usage < low threshold, lower frequency by one level.

So it will immediately jump to the highest frequency, in order to
provide low latency, but will slowly decrease it until it finds the
lowest frequency that provides enough CPU power to support the current
load.

Personally, I prefer conservative, because it isn't as "jumpy", but I
can see ondemand being necessary in a server environment where the
several second lag time to peak performance would hurt response time
when load is low.

--Thomas Tuttle

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Re: The ondemand CPUFreq code -- I hope the functionality stays

[Arjan van de Ven]

> Personally, I prefer conservative, because it isn't as "jumpy", but I
> can see ondemand being necessary in a server environment where the
> several second lag time to peak performance would hurt response time
> when load is low.


jumpy is fine though; at least on the processors my employer makes
changing frequency is really really fast, so you get maximum savings by
switching often (you can switch down more aggressively if you know
you'll switch back up quickly). So switching often is a good policy if
you want both good response AND good power savings... 
I don't know about other cpu makers; my frequency switching machines are
all Intel.

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com