linux-kernel - Re: [PATCH v29 4/4] scsi: ufs: Add HPB 2.0 support

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Date:   Mon, 15 Mar 2021 15:47:02 +0800
From:   Can Guo <cang@...eaurora.org>
To:     daejun7.park@...sung.com
Cc:     Greg KH <gregkh@...uxfoundation.org>, avri.altman@....com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        asutoshd@...eaurora.org, stanley.chu@...iatek.com,
        bvanassche@....org, huobean@...il.com,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        JinHwan Park <jh.i.park@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>,
        SEUNGUK SHIN <seunguk.shin@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>
Subject: Re: [PATCH v29 4/4] scsi: ufs: Add HPB 2.0 support

On 2021-03-15 15:23, Can Guo wrote:
> On 2021-03-15 15:07, Daejun Park wrote:
>>>> This patch supports the HPB 2.0.
>>>> 
>>>> The HPB 2.0 supports read of varying sizes from 4KB to 512KB.
>>>> In the case of Read (<= 32KB) is supported as single HPB read.
>>>> In the case of Read (36KB ~ 512KB) is supported by as 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.
>>>> 
>>>> Signed-off-by: Daejun Park <daejun7.park@...sung.com>
>>>> ---
>>>> +static struct attribute *hpb_dev_param_attrs[] = {
>>>> +        &dev_attr_requeue_timeout_ms.attr,
>>>> +        NULL,
>>>> +};
>>>> +
>>>> +struct attribute_group ufs_sysfs_hpb_param_group = {
>>>> +        .name = "hpb_param_sysfs",
>>>> +        .attrs = hpb_dev_param_attrs,
>>>> +};
>>>> +
>>>> +static int ufshpb_pre_req_mempool_init(struct ufshpb_lu *hpb)
>>>> +{
>>>> +        struct ufshpb_req *pre_req = NULL;
>>>> +        int qd = hpb->sdev_ufs_lu->queue_depth / 2;
>>>> +        int i, j;
>>>> +
>>>> +        INIT_LIST_HEAD(&hpb->lh_pre_req_free);
>>>> +
>>>> +        hpb->pre_req = kcalloc(qd, sizeof(struct ufshpb_req), 
>>>> GFP_KERNEL);
>>>> +        hpb->throttle_pre_req = qd;
>>>> +        hpb->num_inflight_pre_req = 0;
>>>> +
>>>> +        if (!hpb->pre_req)
>>>> +                goto release_mem;
>>>> +
>>>> +        for (i = 0; i < qd; i++) {
>>>> +                pre_req = hpb->pre_req + i;
>>>> +                INIT_LIST_HEAD(&pre_req->list_req);
>>>> +                pre_req->req = NULL;
>>>> +                pre_req->bio = NULL;
>>> 
>>> Why don't prepare bio as same as wb.m_page? Won't that save more time
>>> for ufshpb_issue_pre_req()?
>> 
>> It is pre_req pool. So although we prepare bio at this time, it just
>> only for first pre_req.
> 
> I meant removing the bio_alloc() in ufshpb_issue_pre_req() and 
> bio_put()
> in ufshpb_pre_req_compl_fn(). bios, in pre_req's case, just hold a 
> page.
> So, prepare 16 (if queue depth is 32) bios here, just use them along 
> with
> wb.m_page and call bio_reset() in ufshpb_pre_req_compl_fn(). Shall it 
> work?
> 

If it works, you can even have the bio_add_pc_page() called here. Later 
in
ufshpb_execute_pre_req(), you don't need to call 
ufshpb_pre_req_add_bio_page(),
just call ufshpb_prep_entry() once instead - it save many repeated steps 
for a
pre_req, and you don't even need to call bio_reset() in this case, since 
for a
bio, nothing changes after it is binded with a specific page...

Can Guo.

> Thanks,
> Can Guo.
> 
>> After use it, it should be prepared bio at issue phase.
>> 
>> Thanks,
>> Daejun
>> 
>>> 
>>> Thanks,
>>> Can Guo.
>>> 
>>>> +
>>>> +                pre_req->wb.m_page = alloc_page(GFP_KERNEL | 
>>>> __GFP_ZERO);
>>>> +                if (!pre_req->wb.m_page) {
>>>> +                        for (j = 0; j < i; j++)
>>>> +                                
>>>> __free_page(hpb->pre_req[j].wb.m_page);
>>>> +
>>>> +                        goto release_mem;
>>>> +                }
>>>> +                list_add_tail(&pre_req->list_req, 
>>>> &hpb->lh_pre_req_free);
>>>> +        }
>>>> +
>>>> +        return 0;
>>>> +release_mem:
>>>> +        kfree(hpb->pre_req);
>>>> +        return -ENOMEM;
>>>> +}
>>>> +
>>> 
>>> 
>>>