On Sun, 16 Aug 2009 15:05:30 +0100 Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote: > On Sat, 15 Aug 2009 08:55:17 -0500 > James Bottomley <James.Bottomley@xxxxxxx> wrote: > > > On Sat, 2009-08-15 at 09:22 -0400, Mark Lord wrote: > > > James Bottomley wrote: > > > > > > > > This means you have to drain the outstanding NCQ commands > > > > (stalling the device) before you can send a TRIM. If we do > > > > this for every discard, the performance impact will be pretty > > > > devastating, hence the need to coalesce. It's nothing really > > > > to do with device characteristics, it's an ATA protocol problem. > > > .. > > > > > > I don't think that's really much of an issue -- we already have > > > to do that for cache-flushes whenever barriers are enabled. Yes > > > it costs, but not too much. > > > > That's not really what the enterprise is saying about flush > > barriers. True, not all the performance problems are NCQ queue > > drain, but for a steady workload they are significant. > > Flush barriers are nightmare for more than enterprise. You drive > basically goes for a hike for a bit which trashes interactivity as > well. If the device can't do trim and the like without a drain I > don't see much point doing it at all, except maybe to wait for idle > devices and run a filesystem managed background 'strimmer' thread to > just weed out now idle blocks that have stayed idle - eg by adding an > inode of all the deleted untrimmed blocks and giving it an irregular > empty ? > trim is mostly for ssd's though, and those tend to not have the "goes for a hike" behavior as much...... I wonder if it's worse to batch stuff up, because then the trim itself gets bigger and might take longer..... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
