On Wed 20-02-19 06:23:09, fanchaoting@xxxxxxxxxxxxx wrote: > ############################patch################################# > > commit 16c54688592ce8eea85d2a26d37b64fa07e3e233 > Author: Jan Kara <jack@xxxxxxx> > Date: Fri Sep 30 01:03:17 2016 -0400 > > ext4: Allow parallel DIO reads > > We can easily support parallel direct IO reads. We only have to make > sure we cannot expose uninitialized data by reading allocated block to > which data was not written yet, or which was already truncated. That is > easily achieved by holding inode_lock in shared mode - that excludes all > writes, truncates, hole punches. We also have to guard against page > writeback allocating blocks for delay-allocated pages - that race is > handled by the fact that we writeback all the pages in the affected > range and the lock protects us from new pages being created there. > > Signed-off-by: Jan Kara <jack@xxxxxxx> > Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> > > ############################################################ > > > hi jack , when I checkout lastest kernel > "https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.14.101.tar.xz";. I > use fio to test it , I find io become slowly. Here is my test method: > > # fio -filename=/fio_test -direct=1 -iodepth 1 -thread -rw=randrw > -rwmixread=70 -ioengine=psync -bs=4k -size=5G -numjobs=50 -runtime=180 > -group_reporting -name=randrw_70read_4k > ... > Run status group 0 (all jobs): > READ: bw=29.9MiB/s (31.3MB/s), 29.9MiB/s-29.9MiB/s (31.3MB/s-31.3MB/s), io=5377MiB (5638MB), run=180006-180006msec > WRITE: bw=12.8MiB/s (13.4MB/s), 12.8MiB/s-12.8MiB/s (13.4MB/s-13.4MB/s), io=2303MiB (2415MB), run=180006-180006msec > > when I revert this patch, I find io is faster ... > Run status group 0 (all jobs): > READ: bw=85.3MiB/s (89.4MB/s), 85.3MiB/s-85.3MiB/s (89.4MB/s-89.4MB/s), io=14.0GiB (16.1GB), run=180003-180003msec > WRITE: bw=36.6MiB/s (38.4MB/s), 36.6MiB/s-36.6MiB/s (38.4MB/s-38.4MB/s), io=6587MiB (6907MB), run=180003-180003msec Yes, this is understandable because you direct all 50 threads to do mixed read-write synchronous IO against the same file (I suppose you mount ext4 with dioread_nolock mount option, right?). This commit changes direct IO code to use shared lock on the inode so now reads cannot run in parallel to writes on this file. Honestly, I find the testcase a bit artificial (applications like databases that care about good throughput for mixed read-write workload use AIO which avoids this issue) and the code is simpler this way. Do you have some real use case for this? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
