On 10/13/2017 07:29 PM, Ming Lei wrote: > On Fri, Oct 13, 2017 at 05:08:52PM +0000, Bart Van Assche wrote: >> 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? > > ->can_queue is size of the whole tag space shared by all LUNs, looks it isn't > reasonable to increase cmd_per_lun to .can_queue. > '3' is just a starting point; later on it'll be adjusted via scsi_change_depth(). Looks like it's not working correctly with blk-mq, though. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)
