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Date:   Tue, 06 Apr 2021 13:43:32 +0800
From:   Can Guo <cang@codeaurora.org>
To:     daejun7.park@samsung.com
Cc:     asutoshd@codeaurora.org, nguyenb@codeaurora.org,
        hongwus@codeaurora.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com, ALIM AKHTAR <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Stanley Chu <stanley.chu@mediatek.com>,
        Bean Huo <beanhuo@micron.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Kiwoong Kim <kwmad.kim@samsung.com>,
        Satya Tangirala <satyat@google.com>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] scsi: ufs: Introduce hba performance monitor sysfs
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On 2021-04-06 13:37, Can Guo wrote:
> 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?
> 
>> 
>>> +        }
>>> +
>>> +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.

Sorry, I missunderstood your point... Yes, we can use 
lrbp->compl_time_stamp.

Thanks,
Can Guo.

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