Mike, > The write back throttling (WBT) code checks if REQ_SYNC | REQ_IDLE is > set to determine if a write is O_DIRECT vs buffered. If the bits are > not set then it assumes it's a buffered write and will throttle LIO if > we hit certain metrics. LIO itself is not using the buffer cache and > is doing direct IO, so this has us set the direct bits so we are not > throttled. > > When the initiator application is doing direct IO this can greatly > improve performance. It depends on the backend device but we have seen > where the WBT code is throttling writes to only 20K IOPs with 4K IOs > when the device can support 100K+. Applied to 6.6/scsi-staging, thanks! -- Martin K. Petersen Oracle Linux Engineering
