On Thu, Feb 13, 2020 at 04:34:13PM +0800, Ming Lei wrote: > On Thu, Feb 13, 2020 at 08:24:36AM +0000, Damien Le Moal wrote: > > Got it. And since queue full will mean no more tags, submission will block > > on get_request() and there will be no chance in the elevator to merge > > anything (aside from opportunistic merging in plugs), isn't it ? > > So I guess NVMe HDDs will need some tuning in this area. > > scheduler queue depth is usually 2 times of hw queue depth, so requests > ar usually enough for merging. > > For NVMe, there isn't ns queue depth, such as scsi's device queue depth, > meantime the hw queue depth is big enough, so no chance to trigger merge. Most NVMe devices contain a single namespace anyway, so the shared tag queue depth is effectively the ns queue depth, and an NVMe HDD should advertise queue count and depth capabilities orders of magnitude lower than what we're used to with nvme SSDs. That should get merging and BLK_STS_DEV_RESOURCE handling to occur as desired, right?
