[PATCH v3] scsi: ufs: Fix imprecise load calculation in devfreq window
From: Stanley Chu <hidden>
Date: 2020-06-10 14:42:39
Also in:
linux-mediatek, linux-scsi, lkml
Subsystem:
scsi subsystem, the rest · Maintainers:
"James E.J. Bottomley", "Martin K. Petersen", Linus Torvalds
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 <redacted>
---
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
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