On Fri, 2019-11-22 at 10:14 -0800, Bart Van Assche wrote: > > Hi Ming, > > Thanks for having shared these numbers. I think this is very useful > information. Do these results show the performance drop that happens if > /sys/block/.../device/queue_depth exceeds .can_queue? What I am > wondering about is how important these results are in the context of > this discussion. Are there any modern SCSI devices for which a SCSI LLD > sets scsi_host->can_queue and scsi_host->cmd_per_lun such that the > device responds with BUSY? What surprised me is that only three SCSI > LLDs call scsi_track_queue_full() (mptsas, bfa, esp_scsi). Does that > mean that BUSY responses from a SCSI device or HBA are rare? > Some FC HBAs end up returning busy from ->queuecommand() but I think this is more commonly due to there being and issue with the rport rather than the device. -Ewan
