On Wed, Feb 28, 2018 at 08:28:48PM +0530, Kashyap Desai wrote: > Ming - > > Quick testing on my setup - Performance slightly degraded (4-5% drop)for > megaraid_sas driver with this patch. (From 1610K IOPS it goes to 1544K) > I confirm that after applying this patch, we have #queue = #numa node. > > ls -l > /sys/devices/pci0000:80/0000:80:02.0/0000:83:00.0/host10/target10:2:23/10: > 2:23:0/block/sdy/mq > total 0 > drwxr-xr-x. 18 root root 0 Feb 28 09:53 0 > drwxr-xr-x. 18 root root 0 Feb 28 09:53 1
OK, thanks for your test. As I mentioned to you, this patch should have improved performance on megaraid_sas, but the current slight degrade might be caused by scsi_host_queue_ready() in scsi_queue_rq(), I guess. With .host_tagset enabled and use per-numa-node hw queue, request can be queued to lld more frequently/quick than single queue, then the cost of atomic_inc_return(&host->host_busy) may be increased much meantime, think about millions of such operations, and finally slight IOPS drop is observed when the hw queue depth becomes half of .can_queue. > > > I would suggest to skip megaraid_sas driver changes using shared_tagset > until and unless there is obvious gain. If overall interface of using > shared_tagset is commit in kernel tree, we will investigate (megaraid_sas > driver) in future about real benefit of using it. I'd suggest to not merge it until it is proved that performance can be improved in real device. I will try to work to remove the expensive atomic_inc_return(&host->host_busy) from scsi_queue_rq(), since it isn't needed for SCSI_MQ, once it is done, will ask you to test again. Thanks, Ming
