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

[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?

> > +        }
> > +
> > +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