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

Martin K. Petersen
2021-10-27T17:00:30Z

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