On Fri, 20 Jul 2012, Sarah Sharp wrote:
> > Well, then the device violates the standard for power consumption.
>
> Not necessarily.
>
> Tianyu, are you measuring the whole system power consumption or just the
> power drawn by the device? How are you measuring power consumption?
>
> Also, are you sure the mass storage device was actually suspended?
> Unfortunately, userspace polls unmounted drives every two seconds or so
> to see if there's a medium change. So even though you may have enabled
> auto-suspend, userspace will still be waking the device out of suspend
> every two seconds. That might explain your high suspend power
> consumption.
>
> You would need to unload the mass storage driver to truly measure
> uninterrupted suspend power consumption.
It is possible to disable this polling without unloading usb-storage:
echo 0 >/sys/block/sdX/events_poll_msec
> You can also set the power/autosuspend_delay_ms to something very low,
> like 10, in order to get the mass storage device into suspend faster
> than every two seconds.
Alan Stern
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