On Sat, 2017-10-14 at 00:45 +0800, Ming Lei wrote: > On Fri, Oct 13, 2017 at 04:31:04PM +0000, Bart Van Assche wrote: > > On Sat, 2017-10-14 at 00:07 +0800, Ming Lei wrote: > > > Actually it is in hot path, for example, lpfc and qla2xx's queue depth is 3, > > > > Sorry but I doubt whether that is correct. More in general, I don't know any modern > > storage HBA for which the default queue depth is so low. > > You can grep: > > [ming@ming linux]$ git grep -n cmd_per_lun ./drivers/scsi/ | grep -E "qla2xxx|lpfc" Such a low queue depth will result in suboptimal performance for adapters that communicate over a storage network. I think that's a bug and that both adapters support much higher cmd_per_lun values. (+James Smart) James, can you explain us why commit 445cf4f4d2aa decreased LPFC_CMD_PER_LUN from 30 to 3? Was that perhaps a workaround for a bug in a specific target implementation? (+Himanshu Madhani) Himanshu, do you perhaps know whether it is safe to increase cmd_per_lun for the qla2xxx initiator driver to the scsi_host->can_queue value? > Even SRP/IB isn't big too, just 32. The default value for ib_srp for cmd_per_lun is 62 but that value can be overridden by selecting another value in /etc/default/srp_daemon.conf. Note: a lower value is selected if after SRP login it becomes clear that the target queue depth is lower than the cmd_per_lun value requested by the user. This is a performance optimization and avoids that the SRP target system has to send back BUSY responses to the initiator. Bart.
