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SubjectRe: [PATCH 1/2] scsi: ufs: Introduce hba performance monitor sysfs nodes
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

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