Re: [PATCH] scsi: ufs: revert HPB support

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

On 10/25/21 11:26 AM, Greg Kroah-Hartman wrote:
> Is there a link to where the HPB developer said they would look into
> this?  Perhaps until that happens this should be marked as BROKEN?

Hi Greg,

Daejun wrote the following on Thursday: "I will find out how to make
the HPB code without blk_insert_cloned_request() API." Unfortunately
that email was sent as MIME-encoded so it was only received by the
people Cc-ed on that email and has not been archived by any of the
websites that archives linux-scsi or linux-block emails. The email
that I received is available below. I think it is fine to make this
email public given the presence of two mailing lists in the Cc-list.

Thanks,

Bart.



-------- Forwarded Message --------
Subject: 	Re: please revert the UFS HPB support
Date: 	Fri, 22 Oct 2021 07:41:43 +0900
From: 	박대준 <pdaejun@gmail.com>
To: 	Bart Van Assche <bvanassche@acm.org>
CC: 	Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>, martin.petersen@oracle.com, linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Daejun Park <daejun7.park@samsung.com>, Jaegeuk Kim <jaegeuk@kernel.org>



Hi Bart,

2021년 10월 22일 (금) 오전 1:23, Bart Van Assche <bvanassche@acm.org <mailto:bvanassche@acm.org>>님이 작성:

     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 <mailto: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.


I will find out how to make the HPB code without blk_insert_cloned_request() API.

Thanks,
Daejun