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

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Date:   Wed, 17 Mar 2021 10:45:40 +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 2021-03-17 09:42, Daejun Park wrote:
>> 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...
> 
> Hi, Can Guo
> 
> I tried the idea that you suggested, but it doesn't work properly.
> This optimization should be done next time for enhancement.

Can you elaborate please? Any error seen?

Per my understanding, in the case for pre_reqs, a bio is no different
from a page. Here it can reserve 16 pages for later use, which can be
done the same for bios.

This is not an enhancement, but a doubt - why not? Unless it is not 
doable.

Thanks,
Can Guo.

> 
> Thanks
> Daejun
> 
>> 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;
>>>>>> +}
>>>>>> +
>>>>> 
>>>>> 
>>>>> 
>> 
>> 
>>