On Tue, 2016-09-20 at 10:12 -0400, Alan Stern wrote: > On Tue, 20 Sep 2016, Oliver Neukum wrote: > That shouldn't be an issue in this case, at least, not with the current > code. The sdmmc and memstick drivers block autosuspend if media is > present. Good. > > > > Which means that autosuspend matters only when a card isn't present, > > > and the host is polled every second or so to see whether a card has > > > been inserted. > > > > > > Under those circumstances you probably don't want to use > > > autosuspend. > > > That is, resuming before each poll and suspending afterward may use > > > less energy than staying at full power all the time. > > > > Is that based on concrete figures about power consumption? > > No. Well, I have no idea how to improve this much without hideous overengineering. > > And it seems to me that we need a way to indicate that the heuristics > > should not be used, but a device immediately suspended. The timer > > is sensible only if the next wakeup is unknown. > > The driver can always turn off autosuspend if it wants to. Yes, but this is not the point. A heuristic with a timeout makes sense only if the uses are unpredictable. If you know with a high degree of probability when the next activity comes, you ought to either suspend now or not all until the next activity. Likewise the heuristic is appropriate for leaf nodes. You get nothing from a delay on inner nodes. Any storage (generic sense) device is an inner node. It should suspend immediately after the block device which is the leaf node. 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
