drm/msm: return the average load over the polling period

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: 5a4215e5a3a2 ("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>

diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
index 7418f99e77d9a28090fe877406a5a565dd1593ca..6def0088304637f0f746383a8427dbf20768af5e 100644 (file)
--- 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>
@@ -118,6 +119,8 @@ 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 f531015107c351305db95bc2c5e7b252b8c9ea33..d2539ca78c296be41a5c1dafb3af5f30e701d8dd 100644 (file)
--- 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;
 }