On Wed, 4 Jul 2007, Matthew Garrett wrote:
> On Wed, Jul 04, 2007 at 10:38:47AM -0400, Alan Stern wrote:
>
> > Okay, I agree that (1) can be handled without too much effort. But
> > doing it adds an extra test to _every_ driver's I/O pathway. Freezing
> > userspace does not incur all this additional overhead.
>
> For runtime PM to work it's already necessary to have a test in that
> path to check if the device is suspended. I can't see how this adds any
> overhead to the common case.
Actually it isn't necessary to have a test to check if the device is
suspended. We simply call the autoresume routine; if the device isn't
suspended that routine doesn't have to do anything.
I agree that that the extra test (for system-wide suspend underway) is
needed only if the autoresume fails, which isn't part of the main
pathway. So it doesn't add runtime overhead -- but handling it does
add code overhead.
Alan Stern
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