On Thu, Aug 21, 2008 at 05:00:39PM +1000, Nick Piggin wrote: > On Thursday 21 August 2008 16:14, Dave Chinner wrote: > > > I think that we need to issue explicit unplugs to get the log I/O > > dispatched the way we want on all elevators and stop trying to > > give elevators implicit hints by abusing the bio types and hoping > > they do the right thing.... > > FWIW, my explicit plugging idea is still hanging around in one of > Jens' block trees (actually he refreshed it a couple of months ago). > > It provides an API for VM or filesystems to plug and unplug > requests coming out of the current process, and it can reduce the > need to idle the queue. Needs more performance analysis and tuning > though. We've already got plenty of explicit unplugs in XFS to get stuff moving quickly - I'll just have to add another.... > But existing plugging is below the level of the elevators, and should > only kick in for at most tens of ms at queue idle events, so it sounds > like it may not be your problem. Elevators will need some hint to give > priority to specific requests -- either via the current threads's io > priority, or information attached to bios. It's getting too bloody complex, IMO. What is right for one elevator is wrong for another, so as a filesystem developer I have to pick one to target. With the way the elevators have been regressing, improving and changing behaviour, I am starting to think that I should be picking the noop scheduler. Any 'advanced' scheduler that is slower than the same test on the noop scheduler needs fixing... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
