On Tue, Feb 28, 2012 at 05:56:18PM -0500, Thomas Lynema wrote: > Please reply to my personal email as well as I am not subscribed to the > list. > > I have a PP120GS25SSDR it does support trim > > cat /sys/block/sdc/queue/discard_max_bytes > 2147450880 > > The entire drive is one partition that is totally used by LVM. > > I made a test vg and formatted it with mkfs.xfs. Then mounted it with > discard and got the following result when deleting a kernel source: > > /dev/mapper/ssdvg0-testLV on /media/temp type xfs > (rw,noatime,nodiratime,discard) > > time rm -rf linux-3.2.6-gentoo/ > real 5m7.139s > user 0m0.080s > sys 0m1.580s > I'd say your problem is that trim is extremely slow on your hardware. You've told XFS to execute a discard command for every single extent that is freed, and that can be very slow if you are freeing lots of small extents (like a kernel tree contains) and you have a device that is slow at executing discards. > There where lockups where the system would pause for about a minute > during the process. Yup, that's because it runs as part of the journal commit completion, and if your SSD is extremely slow the journal will stall waiting for all the discards to complete. Basically, online discard is not really a smart thing to use for consumer SSDs. Indeed, it's just not a smart thign to run for most workloads and use cases precisely because discard is a very slow and non-queuable operation on most hardware that supports it. If you really need to run discard, just run a background discard (fstrim) from a cronjob that runs when the system is mostly idle. You won't have any runtime overhead on every unlink but you'll still get the benefit of discarding unused blocks regularly. > ext4 handles this scenerio fine: > > /dev/mapper/ssdvg0-testLV on /media/temp type ext4 > (rw,noatime,nodiratime,discard) > > time rm -rf linux-3.2.6-gentoo/ > > real 0m0.943s > user 0m0.050s > sys 0m0.830s I very much doubt that a single discard IO was issued during that workload - ext4 uses the same fine-grained discard method XFS does, and it does it at journal checkpoint completion just like XFS. So I'd say that ext4 didn't commit the journal during this workload, and no discards were issued, unlike XFS. So, now time how long it takes to run sync to get the discards issued and completed on ext4. Do the same with XFS and see what happens. i.e.: $ time (rm -rf linux-3.2.6-gentoo/ ; sync) is the only real way to compare performance.... > xfs mounted without discard seems to handle this fine: > > /dev/mapper/ssdvg0-testLV on /media/temp type xfs > (rw,noatime,nodiratime) > > time rm -rf linux-3.2.6-gentoo/ > real 0m1.634s > user 0m0.040s > sys 0m1.420s Right, that's how long XFS takes with normal journal checkpoint IO latency. Add to that the time it takes for all the discards to be run, and you've got the above number. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
