[PATCH v3] scsi: ufs: Fix imprecise load calculation in devfreq window

[Stanley Chu]

The UFS load calculation is based on total_time and busy_time in a
devfreq window. However, the precision of both time are different.
busy_time is assigned from "jiffies" thus has different accuracy
from total_time which is assigned from ktime_get().

To guarantee the precision of load calculation, we need to

1. Align time accuracy of both devfreq_dev_status.total_time and
   devfreq_dev_status.busy_time. For example, use "ktime_get()"
   directly.

2. Align below timelines,
   - The beginning time of devfreq windows
   - The beginning of busy time in a new window
   - The end of busy time in the current window

Fixes: a3cd5ec55f6c ("scsi: ufs: add load based scaling of UFS gear")
Signed-off-by: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
---
 drivers/scsi/ufs/ufshcd.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index ad4fc829cbb2..04b79ca66fdf 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1314,6 +1314,7 @@ static int ufshcd_devfreq_get_dev_status(struct device *dev,
 	unsigned long flags;
 	struct list_head *clk_list = &hba->clk_list_head;
 	struct ufs_clk_info *clki;
+	ktime_t curr_t;
 
 	if (!ufshcd_is_clkscaling_supported(hba))
 		return -EINVAL;
@@ -1321,6 +1322,7 @@ static int ufshcd_devfreq_get_dev_status(struct device *dev,
 	memset(stat, 0, sizeof(*stat));
 
 	spin_lock_irqsave(hba->host->host_lock, flags);
+	curr_t = ktime_get();
 	if (!scaling->window_start_t)
 		goto start_window;
 
@@ -1332,18 +1334,17 @@ static int ufshcd_devfreq_get_dev_status(struct device *dev,
 	 */
 	stat->current_frequency = clki->curr_freq;
 	if (scaling->is_busy_started)
-		scaling->tot_busy_t += ktime_to_us(ktime_sub(ktime_get(),
+		scaling->tot_busy_t += ktime_to_us(ktime_sub(curr_t,
 					scaling->busy_start_t));
 
-	stat->total_time = jiffies_to_usecs((long)jiffies -
-				(long)scaling->window_start_t);
+	stat->total_time = ktime_to_us(curr_t) - scaling->window_start_t;
 	stat->busy_time = scaling->tot_busy_t;
 start_window:
-	scaling->window_start_t = jiffies;
+	scaling->window_start_t = ktime_to_us(curr_t);
 	scaling->tot_busy_t = 0;
 
 	if (hba->outstanding_reqs) {
-		scaling->busy_start_t = ktime_get();
+		scaling->busy_start_t = curr_t;
 		scaling->is_busy_started = true;
 	} else {
 		scaling->busy_start_t = 0;
-- 
2.18.0