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Date:   Tue, 06 Apr 2021 13:37:28 +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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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.

> 
>> +                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