Am Montag, 12. Juli 2010, 16:34:11 schrieb Alan Stern: > On Mon, 12 Jul 2010, Oliver Neukum wrote: > > > Am Montag, 12. Juli 2010, 04:02:58 schrieb Alan Stern: > > > On Sun, 11 Jul 2010, Oliver Neukum wrote: > > > > > > > I am afraid this is not quite the case. If the device was just opened and closed, > > > > the normal heuristics make sense. If the device reports that no medium is present, > > > > you should suspend at once. > > > > > > In theory, yes. But how many programs continue to hold the device file > > > open after they learn that no medium is present? And do so without > > > sending more transfer requests? > > > > None that I know of. But do they need to? It seems to me that the normal > > polling will continously open/close devices are a rate comparable to the > > standard time the heuristics uses. > > That statement is a little unclear. Do you mean that the normal > polling programs will open the device file (which automatically sends a > TEST UNIT READY command) and then close the device file each time they > poll for media present? I think that's right; as far as I know they do > not hold the device file open between polls. (If any of them do, they > ought to be changed.) Yes. > I don't see how it affects the topic of this discussion, though. It > means that suspending whenever you learn there is no media will yield > essentially the same result as suspending whenever the device file is > closed. If you suspend as soon as you close, yes. If you use the heuristics of waiting a little time before you suspend, no. > As for the time required... I have thought several times that perhaps > we should have an "autosuspend_ms" attribute in addition to (if not > instead of) the "autosuspend" file. While delays much shorter than 50 > or 100 ms don't make any sense, that still leaves a lot of room between > 50 and 1000 ms, which is the shortest we can currently accomodate. The people at Sony/Ericsson tested that with cdc-acm. No useful power savings. It might be different with storage. Though I see no gain in any delay if we learn that no medium is present. > > Now we could shift this to user space, > > Shift what to user space? Setting delay to 0 as soon as user space learns that no medium is present. > > but I doubt we'd get it in > > in a reasonable time frame. And I believe this is a feature we could > > use in the long run. > > Do you mean we could use autosuspend for storage devices in general, or > that we could use autosuspend whenever no media is present? The feature of a driver letting the core know that the device will be idle from now on for some time. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
