Re: please revert the UFS HPB support

[Bart Van Assche <bvanassche@acm.org>]

On 10/21/21 8:17 AM, Christoph Hellwig wrote:
> On Thu, Oct 21, 2021 at 05:15:20PM +0200, Christoph Hellwig wrote:
>>>> I just noticed the UFS HPB support landed in 5.15, and just as
>>>> before it is completely broken by allocating another request on
>>>> the same device and then reinserting it in the queue.  It is bad
>>>> enough that we have to live with blk_insert_cloned_request for
>>>> dm-mpath, but this is too big of an API abuse to make it into
>>>> a release.  We need to drop this code ASAP, and I can prepare
>>>> a patch for that.
>>>
>>> That sounds awful, do you have a link to the offending commit(s)?
>>
>> I'll need to look for it, busy in calls right now, but just grep for
>> blk_insert_cloned_request.
> 
> Might as well finish the git blame:
> 
> commit 41d8a9333cc96f5ad4dd7a52786585338257d9f1
> Author: Daejun Park <daejun7.park@samsung.com>
> Date:   Mon Jul 12 18:00:25 2021 +0900
> 
>      scsi: ufs: ufshpb: Add HPB 2.0 support
>          
>      Version 2.0 of HBP supports reads of varying sizes from 4KB to 1MB.
> 
>      A read operation <= 32KB is supported as single HPB read. A read between
>      36KB and 1MB is supported by a combination of write buffer command and HPB
>      read command to deliver more PPN. The write buffer commands may not be
>      issued immediately due to busy tags. To use HPB read more aggressively, the
>      driver can requeue the write buffer command. The requeue threshold is
>      implemented as timeout and can be modified with requeue_timeout_ms entry in
>      sysfs.

(+Daejun)

Daejun, can the HPB code be reworked such that it does not use 
blk_insert_cloned_request()? I'm concerned that if the HPB code is not 
reworked that it will be removed from the upstream kernel.

Thanks,

Bart.