[PATCH 5.17 487/772] drm/msm: return the average load over the polling period

Greg Kroah-Hartman
2022-06-07T21:21:38Z

From: Chia-I Wu <olvaffe@gmail.com>

[ Upstream commit 78f815c1cf8fc5f05dc5cec29eb1895cb53470e9 ]

simple_ondemand interacts poorly with clamp_to_idle. It only looks at
the load since the last get_dev_status call, while it should really look
at the load over polling_ms. When clamp_to_idle true, it almost always
picks the lowest frequency on active because the gpu is idle between
msm_devfreq_idle/msm_devfreq_active.

This logic could potentially be moved into devfreq core.

Fixes: 7c0ffcd40b16 ("drm/msm/gpu: Respect PM QoS constraints")
Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Cc: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20220416003314.59211-3-olvaffe@gmail.com
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/msm/msm_gpu.h | 3 ++
drivers/gpu/drm/msm/msm_gpu_devfreq.c | 60 ++++++++++++++++++++++++++-
2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
index a88ec0fc6d87..5efca011d66f 100644
--- a/drivers/gpu/drm/msm/msm_gpu.h
+++ b/drivers/gpu/drm/msm/msm_gpu.h
@@ -9,6 +9,7 @@

#include <linux/adreno-smmu-priv.h>
#include <linux/clk.h>
+#include <linux/devfreq.h>
#include <linux/interconnect.h>
#include <linux/pm_opp.h>
#include <linux/regulator/consumer.h>
@@ -114,6 +115,8 @@ struct msm_gpu_devfreq {
/** idle_time: Time of last transition to idle: */
ktime_t idle_time;

+ struct devfreq_dev_status average_status;
+
/**
* idle_work:
*
diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
index d2b4c646a0ae..c7dbaa4b1926 100644
--- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
+++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
@@ -9,6 +9,7 @@

#include <linux/devfreq.h>
#include <linux/devfreq_cooling.h>
+#include <linux/math64.h>
#include <linux/units.h>

/*
@@ -75,12 +76,69 @@ static void get_raw_dev_status(struct msm_gpu *gpu,
status->busy_time = busy_time;
}

+static void update_average_dev_status(struct msm_gpu *gpu,
+ const struct devfreq_dev_status *raw)
+{
+ struct msm_gpu_devfreq *df = &gpu->devfreq;
+ const u32 polling_ms = df->devfreq->profile->polling_ms;
+ const u32 max_history_ms = polling_ms * 11 / 10;
+ struct devfreq_dev_status *avg = &df->average_status;
+ u64 avg_freq;
+
+ /* simple_ondemand governor interacts poorly with gpu->clamp_to_idle.
+ * When we enforce the constraint on idle, it calls get_dev_status
+ * which would normally reset the stats. When we remove the
+ * constraint on active, it calls get_dev_status again where busy_time
+ * would be 0.
+ *
+ * To remedy this, we always return the average load over the past
+ * polling_ms.
+ */
+
+ /* raw is longer than polling_ms or avg has no history */
+ if (div_u64(raw->total_time, USEC_PER_MSEC) >= polling_ms ||
+ !avg->total_time) {
+ *avg = *raw;
+ return;
+ }
+
+ /* Truncate the oldest history first.
+ *
+ * Because we keep the history with a single devfreq_dev_status,
+ * rather than a list of devfreq_dev_status, we have to assume freq
+ * and load are the same over avg->total_time. We can scale down
+ * avg->busy_time and avg->total_time by the same factor to drop
+ * history.
+ */
+ if (div_u64(avg->total_time + raw->total_time, USEC_PER_MSEC) >=
+ max_history_ms) {
+ const u32 new_total_time = polling_ms * USEC_PER_MSEC -
+ raw->total_time;
+ avg->busy_time = div_u64(
+ mul_u32_u32(avg->busy_time, new_total_time),
+ avg->total_time);
+ avg->total_time = new_total_time;
+ }
+
+ /* compute the average freq over avg->total_time + raw->total_time */
+ avg_freq = mul_u32_u32(avg->current_frequency, avg->total_time);
+ avg_freq += mul_u32_u32(raw->current_frequency, raw->total_time);
+ do_div(avg_freq, avg->total_time + raw->total_time);
+
+ avg->current_frequency = avg_freq;
+ avg->busy_time += raw->busy_time;
+ avg->total_time += raw->total_time;
+}
+
static int msm_devfreq_get_dev_status(struct device *dev,
struct devfreq_dev_status *status)
{
struct msm_gpu *gpu = dev_to_gpu(dev);
+ struct devfreq_dev_status raw;

- get_raw_dev_status(gpu, status);
+ get_raw_dev_status(gpu, &raw);
+ update_average_dev_status(gpu, &raw);
+ *status = gpu->devfreq.average_status;

return 0;
}
--
2.35.1