Re: [PATCH v2] scsi: sr: use block layer runtime PM

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On Sat, 7 Sep 2013, Aaron Lu wrote:

> >>> Note that due to ODD will be polled every 2 seconds,
> >>
> >> Since the device will be polled every 2 seconds
> >>
> >>>  for suspend to
> >>> actually happen, the autosuspend_delay can not be set to more than 2
> >>> seconds or the polling interval has to be increased.
> >>
> >> Is this true?  What about event driven devices?  Supposing a distro has
> >> a different interval.
> >>
> >> How about
> >>
> >> If your Distribution polls the device, the autosuspend interval cannot
> >> be set to longer than the polling interval otherwise the device will
> >> never suspend.
> > 
> > The default polling done by the kernel uses 2-second intervals.  Of 
> > course, distributions and users can change this or disable it entirely.
> 
> What about:
> Note that due to the device will be polled by kernel at a constant
> interval specified at /sys/module/block/parameters/events_dfl_poll_msecs,
> the default value is 2 seconds, the autosuspend delay cannot be set to
> longer than the polling interval otherwise the device will never suspend.

Well, I wouldn't say "cannot" -- people can set the delay to whatever
they want.  Just: If the autosuspend delay is set longer than the
polling interval then the device will never suspend.

Also, the actual polling interval is controlled by
/sys/block/sdX/events_poll_msec.  The file you mentioned merely
contains the default polling interval used for new devices.

Alan Stern

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