The ati petition

[Alex Deucher]

On Mon, 6 Sep 2004 20:31:04 -0400 (EDT), Vladimir Dergachev
<volodya at mindspring.com> wrote:
> 
> 
> On Mon, 6 Sep 2004, Mathieu Lacage wrote:
> 
> > On Mon, 2004-09-06 at 02:23, Vladimir Dergachev wrote:
> >>>>> to the same power-performance tradeoff for your graphics card and saving
> >>>>> power.
> >>>> Good point. I would imagine that since most of GPU is inactive under
> >>>> regular X drivers I am running at minimum power ;)
> >>>
> >>> Unlikely.  I suspect that, like with the CPU, the GPU speed must be
> >>>  manually slowed.
> >>
> >> Unlike regular CPU, GPU consists of many blocks. I would expect that if 3d
> >> engine is not used at all it consumes little power - kinda like running
> >> HLT continuously on spare CPU.
> >
> > Actually, that is pretty unlikely. A lot of the power consumption of
> > these devices (even when they are running at full speed) comes from the
> > clock tree which distributes the clock throughout the chip. Unless the
> > designers have added special multiplexers to stop completely the clock
> > tree of the unused blocks, these will consume a lot of power even idle.
> 
> Possibly they did. There are registers in the documentation that deal with
> power management and they have bits like this:
> 
>     RE_CLK:     0   - Dynamic
>                 1   - Force on
> 
> To me this would mean that the RE (Render Engine) clock is not active if
> there is nothing for the render engine to do.
> 
> Keep in mind that this is mere speculation. Also, some ATI sample code
> writes 1 to such registers with comment that "some versions of ASIC do not
> properly implement dynamic clocks". Linux drivers do not have this code
> though, so this might have been fixed in production version.

I recently applied a patch from ati for enabling dynamic clock scaling
to xorg cvs.  enable it with option "DynamicClocks".  it provides a
noticeable increase in battery life on my m6 laptop.

Alex

> 
>                          best
> 
>                            Vladimir Dergachev
> 
> > The basic clock rate used nowadays is high enough and the area of the
> > chip die is big enough that these issues are non-negligeable. Of course,
> > restarting the stopped blocks can also be a bit tricky for the chip
> > designers.
> >
> > Another rather popular technique is to step the clock speed but that is
> > much more complex to implement for the designers which is why few ASICs
> > really do it.
> >
> > Of course, this is off-topic but I could not resist. Bad bad me. It
> > should be said I have minimum experience in this domain so, the usual
> > disclaimers apply.
> >
> > regards,
> > Mathieu
> > --
> > Mathieu Lacage <mathieu at gnu.org>
> >
> >
> > _______________________________________________
> > xorg mailing list
> > xorg at freedesktop.org
> > http://freedesktop.org/mailman/listinfo/xorg
> >
> 
> 
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