Re: Processor C states and USB problem

[Petr Olivka <petr.olivka-jmYXjVuSQ4U@public.gmane.org>]

I did ask about this problem in usb-devel-forum.

You can see answer:
http://sourceforge.net/mailarchive/message.php?msg_id=6249537

usb host use poll mode to get data from usb peripherals, and result is
continuous busmaster activity.

poli


On Mon, 5 Jan 2004 mike-Z92qn3yYq0hWk0Htik3J/w@public.gmane.org wrote:

> Recently I had problems with my network card and ACPI (see earlier posts for
> the problem and solution) so I thought I'd take a closer look at ACPI on
> this notebook (Acer Travelmate 800).
>
> Looking at the proc entries for the processor I saw the following.
>
> active state:            C3
> default state:           C1
> bus master activity:     80070020
> states:
>    C1:                  promotion[C2] demotion[--] latency[000]
> usage[00000010]
>    C2:                  promotion[C3] demotion[C1]
> latency[001]usage[01077887]
>   *C3:                  promotion[--] demotion[C2] latency[085]
> usage[00083507]
>
> This looked pretty normal to me, apart from the fact that the processor was
> spending a lot of time in C3 although the notebook was idle.
>
> Now I plugged in my USB mouse.
>
> cat /proc/acpi/processor/CPU0/power
> active state:            C2
> default state:           C1
> bus master activity:     ffffffff <---- USB is active
> states:
>    C1:                  promotion[C2] demotion[--] latency[000]
> usage[00000010]
>   *C2:                  promotion[C3] demotion[C1]
> latency[001]usage[00871647]
>    C3:                  promotion[--] demotion[C2] latency[085]
> usage[00077386]
>
> The processor never left the C2 state.
> After unplugging the mouse "bus master activity" showed normal values again.
>
> Now for my two questions:
>
> 1.) Is it normal for the notebook to spend so much time in C3, even if it is
> idle?
>
> 2.) Why is an USB device screwing up the bus master activity, resulting in
> the processor never leaving C2?
>
>
> /Michael
>
>
>
>
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