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Subject: Re: [RFC PATCH v2 4/5] scsi: ufs: L2P map management for HPB read
Reply-To: daejun7.park@samsung.com
From:   Daejun Park <daejun7.park@samsung.com>
To:     Bean Huo <huobean@gmail.com>,
        Daejun Park <daejun7.park@samsung.com>,
        ALIM AKHTAR <alim.akhtar@samsung.com>,
        "avri.altman@wdc.com" <avri.altman@wdc.com>,
        "jejb@linux.ibm.com" <jejb@linux.ibm.com>,
        "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
        "asutoshd@codeaurora.org" <asutoshd@codeaurora.org>,
        "beanhuo@micron.com" <beanhuo@micron.com>,
        "stanley.chu@mediatek.com" <stanley.chu@mediatek.com>,
        "cang@codeaurora.org" <cang@codeaurora.org>,
        "bvanassche@acm.org" <bvanassche@acm.org>,
        "tomas.winkler@intel.com" <tomas.winkler@intel.com>
CC:     "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@samsung.com>,
        Sung-Jun Park <sungjun07.park@samsung.com>,
        yongmyung lee <ymhungry.lee@samsung.com>,
        Jinyoung CHOI <j-young.choi@samsung.com>,
        Adel Choi <adel.choi@samsung.com>,
        BoRam Shin <boram.shin@samsung.com>
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Date:   Tue, 16 Jun 2020 10:17:44 +0900
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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