On Fri, 2010-10-08 at 12:04 +0200, ext Wu, Xia wrote: > On Fri, Oct 08, 2010 at 04:35:14PM +0800, Yong Wang wrote: > > > sync_supers task currently wakes up periodically for superblock > > > writeback. This hurts power on battery driven devices. This patch > > > turns this housekeeping timer into a deferable timer so that it > > > does not fire when system is really idle. > > > How long can the timer be defereed? We can't simply stop writing > > out data for a long time. I think the current timer value should be > > the upper bound, but allowing to fire earlier to run during the > > same wakeup cycle as others is fine. > > If the system is in sleep state, this timer can be deferred to the next wake-up interrupt. > If the system is busy, this timer will fire at the scheduled time. However, when the next wake-up interrupt happens is not defined. It can happen 1ms after, or 1 minute after, or 1 hour after. What Christoph says is that there should be some guarantee that sb writeout starts, say, within 5 to 10 seconds interval. Deferrable timers do not guarantee this. But take a look at the range hrtimers - they do exactly this. -- Best Regards, Artem Bityutskiy (ÐÑÑÑÐ ÐÐÑÑÑÐÐÐ) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>