hpsa: honor queue depth of physical devices
When using the ioaccel submission methods, requests destined for RAID volumes are sometimes diverted to physical devices. The OS has no or limited knowledge of these physical devices, so it is up to the driver to avoid pushing the device too hard. It is better to honor the physical device queue limit rather than making the device spew zillions of TASK SET FULL responses. This is so that hpsa based devices support /sys/block/sdNN/device/queue_type of simple, which lets the SCSI midlayer automatically adjust the queue_depth based on TASK SET FULL and GOOD status. Adjust the queue depth for a new device after it is created based on the maximum queue depths of the physical devices that constitute the device. This drops the maximum queue depth from .can_queue of 1024 to something like 174 for single-drive RAID-0, 348 for two-drive RAID-1, etc. It also adjusts for the ratio of data to parity drives. Reviewed-by: NScott Teel <scott.teel@pmcs.com> Signed-off-by: NWebb Scales <webbnh@hp.com> Signed-off-by: NDon Brace <don.brace@pmcs.com> Signed-off-by: NChristoph Hellwig <hch@lst.de>
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