Re: Processor C states and USB problem

[Michael Guntsche <mike-Z92qn3yYq0hWk0Htik3J/w@public.gmane.org>]

On Wed, 14 Jan 2004 08:55:35 +0100
Diego SANTA CRUZ <dsanta-W/9V78bTXrinCNX9eg9BBA@public.gmane.org> wrote:

> On Wed, 2004-01-14 at 03:10, Yu, Luming wrote:
> > > > > I picked up this thread and I'm interested in knowing a 
> > > bit more about
> > > > > bus mastering and C3, as my laptop never goes into C3. I 
> > > own a Dell
> > > > > Inspiron 8500 (details at
> > > > > http://ltswww.epfl.ch/~dsanta/resources/dell-i8500-linux).
> > > > > 
> > 
> > How did you know your processor never transition to C3 mode?
> > 
> 
> The usage count is never above 5, even after a long period (an hour or
> more of idle CPU). But yes, strictly speaking it's almost never ;-)
> 
> > > > > This is what I get for the power states:
> > > > > # cat /proc/acpi/processor/CPU0/power
> > > > > active state:            C2
> > > > > default state:           C1
> > > > > bus master activity:     ffffffff
> > > > > states:
> > > > >     C1:                  promotion[C2] demotion[--] 
> > > > > latency[000] usage[00039800]
> > > > >    *C2:                  promotion[C3] demotion[C1] 
> > > > > latency[050] usage[00573330]
> > > > >     C3:                  promotion[--] demotion[C2] 
> > > > > latency[050] usage[00000004]
> > > > > 
> > 
> > Usage of C3 is 4. 
> 
> Yes, but compared to the usage count of C2 that is extremely low, and
> the CPU is idling all the time (CPU usage is below 1%). I don't know
> much about C states but I guess it should go into C3 much more often,
> and the bus mastering activity should show something else than
> ffffffff when booting with a bare bones kernel and with no extra hw
> initialized(USB, FireWire, etc.)
> 

Have you tried running a 2.6 kernel?
Under 2.4 bus master always shows "ffffffff" on my notebook. Sometimes
shutting down USB helps, sometimes it doesn't.
Running under 2.6 I only get full bus master activity if an USB
mouse is plugged in.


/michael


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