On 10/25/10 22:59, Vivek Goyal wrote: > Richard, > > So what problem are you facing? I know you are referring to CFQ ioprio not > working with dm targets but how does it impact you? So it is not about > overall disk performance or any slow down with dm-crypt target but just > about prioritizing your IO over other? The ioprio not working is probably the biggest problem (since it is used quite a lot for background tasks like desktop indexing services). But also the overall performance is worse. I didn't do a rigorous benchmarking, but tried a following simple test to see the impact of my dm-crypt patch: test-write: SIZE=640 KERN=`uname -r` ((time /bin/bash -c "dd if=/dev/zero bs=1M count=64 \ of=normal.tst oflag=direct") 1>$KERN-write-normal 2>&1) | ((time /bin/bash -c "ionice -c 3 dd if=/dev/zero bs=1M \ count=64 of=idle.tst oflag=direct") 1>$KERN-write-idle 2>&1) Times for vanilla kernel (with CFQ) were 5.24s for idle and 5.38s for normal, times for patched kernel were 4.9s for idle and 3.13s for normal. A similar test for reading showed even bigger differences: vanilla kernel has 8.5s for idle as well as 8.5s for normal, patched kernel has 4.2s for idle and 2.1s for normal. So it seems that CFQ is behaving really badly if it is not able to see which process is doing the IO (and sees kcryptd everywhere). As far as I understood, there is no point in using CFQ in that case and it is much better to use other scheduler in this situation. Richard -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
