Re: [RFC PATCH v2 4/5] scsi: ufs: L2P map management for HPB read

[Daejun Park <daejun7.park@samsung.com>]

Hi Bean
> 
> 
> On Mon, 2020-06-15 at 18:30 +0900, Daejun Park wrote:
> > +static int ufshpb_execute_map_req(struct ufshpb_lu *hpb,
> > +                                 struct ufshpb_req *map_req)
> > +{
> > +       struct request_queue *q;
> > +       struct request *req;
> > +       struct scsi_request *rq;
> > +       int ret = 0;
> > +
> > +       q = hpb->sdev_ufs_lu->request_queue;
> > +       ret = ufshpb_map_req_add_bio_page(hpb, q, map_req->bio,
> > +                                         map_req->mctx);
> > +       if (ret) {
> > +               dev_notice(&hpb->hpb_lu_dev,
> > +                          "map_req_add_bio_page fail %d - %d\n",
> > +                          map_req->rgn_idx, map_req->srgn_idx);
> > +               return ret;
> > +       }
> > +
> > +       req = map_req->req;
> > +
> > +       blk_rq_append_bio(req, &map_req->bio);
> > +
> > +       req->timeout = 0;
> > +       req->end_io_data = (void *)map_req;
> > +
> > +       rq = scsi_req(req);
> > +       ufshpb_set_read_buf_cmd(rq->cmd, map_req->rgn_idx,
> > +                               map_req->srgn_idx, hpb-
> > >srgn_mem_size);
> > +       rq->cmd_len = HPB_READ_BUFFER_CMD_LENGTH;
> > +
> > +       blk_execute_rq_nowait(q, NULL, req, 1,
> > ufshpb_map_req_compl_fn);
> 
> 
> HPB map_req is now being en-queued in sdev->request_queue.
> This is ok for the HPB v1.0. Have you ever been thinking about
> changing this way to directly issue HPB requests to UFS?
I think it is enough to support HPB.

> Actually, there are two reasons for this way:
> 
> 1. Latency of loading mapping entries is lower comparing to your curret
> approach.
Our map request style utilizes block layer API. It makes the codes keep
simple and reliable. Also, I think the latency of loading mapping entries 
is not critical for HPB. Futhermore, I think the other requests from
user is important than loading mapping entries. If the map_work issues map
request directly, the user requests can be disturbed by map requests.

> 2. Also, it is preparing for the HPB v2.0.  After all HPB 1.0 only
> supports 4KB read, this is useless, I am looking for the HPB v2.0.
I don't understand this comment. In HPB v2.0, this code can be used without
changing.

Thanks,
Daejun