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Date:   Tue, 06 Apr 2021 14:11:19 +0800
From:   Can Guo <cang@codeaurora.org>
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Subject: Re: [PATCH 1/2] scsi: ufs: Introduce hba performance monitor sysfs
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On 2021-04-06 13:58, Daejun Park wrote:
> Hi Can Guo,
>> 
>> Hi Daejun,
>> 
>> On 2021-04-06 12:11, Daejun Park wrote:
>>> Hi Can Guo,
>>> 
>>>> +static ssize_t monitor_enable_store(struct device *dev,
>>>> +                                    struct device_attribute *attr,
>>>> +                                    const char *buf, size_t count)
>>>> +{
>>>> +        struct ufs_hba *hba = dev_get_drvdata(dev);
>>>> +        unsigned long value, flags;
>>>> +
>>>> +        if (kstrtoul(buf, 0, &value))
>>>> +                return -EINVAL;
>>>> +
>>>> +        value = !!value;
>>>> +        spin_lock_irqsave(hba->host->host_lock, flags);
>>>> +        if (value == hba->monitor.enabled)
>>>> +                goto out_unlock;
>>>> +
>>>> +        if (!value) {
>>>> +                memset(&hba->monitor, 0, sizeof(hba->monitor));
>>>> +        } else {
>>>> +                hba->monitor.enabled = true;
>>>> +                hba->monitor.enabled_ts = ktime_get();
>>> 
>>> How about setting lat_max to and lat_min to KTIME_MAX and 0?
>> 
>> lat_min is already 0. What is the benefit of setting lat_max to
>> KTIME_MAX?
>> 
>>> I think lat_sum should be 0 at this point.
>> 
>> lat_sum is already 0 at this point, what is the problem?
> 
> Sorry. I misunderstood about resetting monitor values.
> 
>> 
>>> 
>>>> +        }
>>>> +
>>>> +out_unlock:
>>>> +        spin_unlock_irqrestore(hba->host->host_lock, flags);
>>>> +        return count;
>>>> +}
>>> 
>>> 
>>>> +static void ufshcd_update_monitor(struct ufs_hba *hba, struct
>>>> ufshcd_lrb *lrbp)
>>>> +{
>>>> +        int dir = ufshcd_monitor_opcode2dir(*lrbp->cmd->cmnd);
>>>> +
>>>> +        if (dir >= 0 && hba->monitor.nr_queued[dir] > 0) {
>>>> +                struct request *req = lrbp->cmd->request;
>>>> +                struct ufs_hba_monitor *m = &hba->monitor;
>>>> +                ktime_t now, inc, lat;
>>>> +
>>>> +                now = ktime_get();
>>> 
>>> How about using lrbp->compl_time_stamp instead of getting new value?
>> 
>> I am expecting "now" keeps increasing and use it to update
>> m->busy_start_s,
>> but if I use lrbp->compl_time_stamp to do that, below line ktime_sub()
>> may
>> give me an unexpected value as lrbp->compl_time_stamp may be smaller
>> than
>> m->busy_start_ts, because the actual requests are not completed by the
>> device
>> in the exact same ordering as the bits set in hba->outstanding_tasks,
>> but driver
>> is completing them from bit 0 to bit 31 in ascending order.
> 
> lrbp->compl_time_stamp is set just before calling 
> ufshcd_update_monitor().
> And I don't think it can be negative value, because 
> ufshcd_send_command()
> and __ufshcd_transfer_req_compl() are protected by host lock.
> 

Yes, I replied u in another mail... I will use the compl_time_stamp in 
next
version. And later I will add alloc_time_stamp and release_time_stamp to 
lrbp
so that we can monitor the overall send/compl path, including hpb_prep() 
and
hpb_rsp().

>> 
>>> 
>>>> +                inc = ktime_sub(now, m->busy_start_ts[dir]);
>>>> +                m->total_busy[dir] = ktime_add(m->total_busy[dir],
>>>> inc);
>>>> +                m->nr_sec_rw[dir] += blk_rq_sectors(req);
>>>> +
>>>> +                /* Update latencies */
>>>> +                m->nr_req[dir]++;
>>>> +                lat = ktime_sub(now, lrbp->issue_time_stamp);
>>>> +                m->lat_sum[dir] += lat;
>>>> +                if (m->lat_max[dir] < lat || !m->lat_max[dir])
>>>> +                        m->lat_max[dir] = lat;
>>>> +                if (m->lat_min[dir] > lat || !m->lat_min[dir])
>>>> +                        m->lat_min[dir] = lat;
>>> 
>>> This if statement can be shorted, by setting lat_max / lat_min as
>>> default value.
>> 
>> I don't quite get it, can you show me the code sample?
> 
> I think " || !m->lat_max[dir]" can be removed.
> 
>                 if (m->lat_max[dir] < lat)
>                         m->lat_max[dir] = lat;
>                 if (m->lat_min[dir] > lat)
>                         m->lat_min[dir] = lat;
> 

 From the beginning, lat_min is 0, without "!m->lat_min[dir]", m->lat_min
will never be updated. Same for lat_max. Meanwhile, !m->lat_min/max will
be hit only once in each round, which does not hurt.

Thanks,
Can Guo.

> Thanks,
> Daejun
> 
>> 
>> Thanks,
>> Can Guo
>> 
>>> 
>>>> +
>>>> +                m->nr_queued[dir]--;
>>>> +                /* Push forward the busy start of monitor */
>>>> +                m->busy_start_ts[dir] = now;
>>>> +        }
>>>> +}
>>> 
>>> Thanks,
>>> Daejun