Re: uhci vs ehci: 5 wakeups/s saved

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Wed, 3 Oct 2007, Alan Jenkins wrote:

> So if I want to find out why ehci causes more wakeups on an idle system 
> than uhci, I need to break down the ehci_watchdog timer into its 
> component uses.

One other thing I forgot to mention.  As you know, ehci-hcd's extra
interrupts tell the driver it can disable DMA.  But uhci-hcd never
disables DMA as long as any active devices are plugged into the
controller.  The hardware doesn't permit it.  So even though uhci-hcd's
overall interrupt count may be lower, it forces the CPU to stay out of
the deep sleep states that ehci-hcd allows for.

Alan Stern


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