Re: [PATCH] scsi: ufs: mark HPB support as BROKEN

Ming,

What I meant is to use one totally ufshpb private command allocated
from private slab to replace the spawned request, which is sent to
ufshcd_queuecommand() directly, so forward progress is guaranteed if
the blk-mq request's tag can be reused for issuing this private
command. This approach takes a bit effort, but avoids tags
reservation.

Yep, I was just noting that error handling was a better example than the
ioctl given the context.

1) how many queue depth for the hba? If it is small, even 1 reservation
can affect performance.

Indeed. But there is no free lunch.

2) how many inflight write buffer commands are to be supported? Or how
many is enough for obtaining expected performance? If the number is
big, reserved tags can't work.

That really is something the UFS developers need to work out. I am not
sure whether permanently pinning down memory is a bigger problem than
queue tags being a finite resource.

-- 
Martin K. Petersen	Oracle Linux Engineering