Hi Ted & Jan, I've observed an significant performance regression with the following commit in my Intel P3600 NVMe SSD. 16c54688592c ext4: Allow parallel DIO reads >From my initial investigation, it may be because of the inode_lock_shared (down_read) consumes more than inode_lock (down_write) in mixed random read write workload. Here is my test result. ioengine=psync direct=1 rw=randrw iodepth=1 numjobs=8 size=20G runtime=600 w/ parallel dio reads : kernel 5.2.0 w/o parallel dio reads: kernel 5.2.0, then revert the following commits: 1d39834fba99 ext4: remove EXT4_STATE_DIOREAD_LOCK flag (related) e5465795cac4 ext4: fix off-by-one error when writing back pages before dio read (related) 16c54688592c ext4: Allow parallel DIO reads bs=4k: ------------------------------------------------------------------------------------------- w/ parallel dio reads | READ 30898KB/s, 7724, 555.00us | WRITE 30875KB/s, 7718, 479.70us ------------------------------------------------------------------------------------------- w/o parallel dio reads| READ 117915KB/s, 29478, 248.18us | WRITE 117854KB/s，29463, 21.91us ------------------------------------------------------------------------------------------- bs=16k: ------------------------------------------------------------------------------------------- w/ parallel dio reads | READ 58961KB/s, 3685, 835.28us | WRITE 58877KB/s, 3679, 1335.98us ------------------------------------------------------------------------------------------- w/o parallel dio reads| READ 218409KB/s, 13650, 554.46us | WRITE 218257KB/s，13641, 29.22us ------------------------------------------------------------------------------------------- bs=64k: ------------------------------------------------------------------------------------------- w/ parallel dio reads | READ 119396KB/s, 1865, 1759.38us | WRITE 119159KB/s, 1861, 2532.26us ------------------------------------------------------------------------------------------- w/o parallel dio reads| READ 422815KB/s, 6606, 1146.05us | WRITE 421619KB/s, 6587, 60.72us ------------------------------------------------------------------------------------------- bs=512k: ------------------------------------------------------------------------------------------- w/ parallel dio reads | READ 392973KB/s, 767, 5046.35us | WRITE 393165KB/s, 767, 5359.86us ------------------------------------------------------------------------------------------- w/o parallel dio reads| READ 590266KB/s, 1152, 4312.01us | WRITE 590554KB/s, 1153, 2606.82us ------------------------------------------------------------------------------------------- bs=1M: ------------------------------------------------------------------------------------------- w/ parallel dio reads | READ 487779KB/s, 476, 8058.55us | WRITE 485592KB/s, 474, 8630.51us ------------------------------------------------------------------------------------------- w/o parallel dio reads| READ 593927KB/s, 580, 7623.63us | WRITE 591265KB/s, 577, 6163.42us ------------------------------------------------------------------------------------------- Thanks, Joseph
