Hi Jagan, On Wed, Jan 18, 2012 at 11:30:54AM -0800, Jagan Reddy wrote: > Joe, > Thanks for looking into the issue and running the tests and suggesting to use "direct" flag. I do see a difference with "direct" flag using dd. However the difference is significant when using bs=64M compared to bs=4k. I've spent a couple of days tinkering with aio-stress and thinp on ramdisks. More tests can be found here: https://github.com/jthornber/thinp-test-suite/blob/master/ramdisk_tests.rb It appears that wiping the device (ie. to ensure total allocation) is causing the issue, and what's more this is a more general problem than just thinp. For instance see this test: def test_linear_aio_stress linear_table = Table.new(Linear.new(@volume_size, @data_dev, 0)) @dm.with_dev(linear_table) do |linear_dev| aio_stress(linear_dev) wipe_device(linear_dev) # cause slow down aio_stress(linear_dev) end end For me, the first run of aio_stress manages a throughput of ~9G/s. After the wipe, which is just a simple dd across the device, performance drops to ~5.5 G/s. Also throughput on the device under the linear target also drops. Permanently. I don't know if this is specific to aio, or a more general slowdown. Once we have got to the bottom of this I've written a couple of experimental patches that we can try to boost read performance further. - Joe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
