On 19/8/23 15:57, Joseph Qi wrote: > Hi Dave, > > On 19/8/22 13:40, Dave Chinner wrote: >> On Wed, Aug 21, 2019 at 09:04:57AM +0800, Joseph Qi wrote: >>> Hi Ted， >>> >>> On 19/8/21 00:08, Theodore Y. Ts'o wrote: >>>> On Tue, Aug 20, 2019 at 11:00:39AM +0800, Joseph Qi wrote: >>>>> >>>>> I've tested parallel dio reads with dioread_nolock, it doesn't have >>>>> significant performance improvement and still poor compared with reverting >>>>> parallel dio reads. IMO, this is because with parallel dio reads, it take >>>>> inode shared lock at the very beginning in ext4_direct_IO_read(). >>>> >>>> Why is that a problem? It's a shared lock, so parallel threads should >>>> be able to issue reads without getting serialized? >>>> >>> The above just tells the result that even mounting with dioread_nolock, >>> parallel dio reads still has poor performance than before (w/o parallel >>> dio reads). >>> >>>> Are you using sufficiently fast storage devices that you're worried >>>> about cache line bouncing of the shared lock? Or do you have some >>>> other concern, such as some other thread taking an exclusive lock? >>>> >>> The test case is random read/write described in my first mail. And >> >> Regardless of dioread_nolock, ext4_direct_IO_read() is taking >> inode_lock_shared() across the direct IO call. And writes in ext4 >> _always_ take the inode_lock() in ext4_file_write_iter(), even >> though it gets dropped quite early when overwrite && dioread_nolock >> is set. But just taking the lock exclusively in write fro a short >> while is enough to kill all shared locking concurrency... >> >>> from my preliminary investigation, shared lock consumes more in such >>> scenario. >> >> If the write lock is also shared, then there should not be a >> scalability issue. The shared dio locking is only half-done in ext4, >> so perhaps comparing your workload against XFS would be an >> informative exercise... > > I've done the same test workload on xfs, it behaves the same as ext4 > after reverting parallel dio reads and mounting with dioread_lock. A typo here, s/dioread_lock/dioread_nolock/ > Here is the test result: > psync, randrw, direct=1, numofjobs=8 > > 4k: > ----------------------------------------- > ext4 | READ 123450KB/s | WRITE 123368KB/s > ----------------------------------------- > xfs | READ 123848KB/s | WRITE 123761KB/s > ----------------------------------------- > > 16k: > ----------------------------------------- > ext4 | READ 222477KB/s | WRITE 222322KB/s > ----------------------------------------- > xfs | READ 223261KB/s | WRITE 223106KB/s > ----------------------------------------- > > 64k: > ----------------------------------------- > ext4 | READ 427406KB/s | WRITE 426197KB/s > ----------------------------------------- > xfs | READ 403697KB/s | WRITE 402555KB/s > ----------------------------------------- > > 512k: > ----------------------------------------- > ext4 | READ 618752KB/s | WRITE 619054KB/s > ----------------------------------------- > xfs | READ 614954KB/s | WRITE 615254KB/s > ----------------------------------------- > > 1M: > ----------------------------------------- > ext4 | READ 615011KB/s | WRITE 612255KB/s > ----------------------------------------- > xfs | READ 624087KB/s | WRITE 621290KB/s > ----------------------------------------- >
