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

[Can Guo]

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