drm: Measure Self Refresh Entry/Exit times to avoid thrashing

Currently the self refresh idle timer is a const set by the crtc. This
is fine if the self refresh entry/exit times are well-known for all
panels used on that crtc. However panels and workloads can vary quite a
bit, and a timeout which works well for one doesn't work well for
another.

In the extreme, if the timeout is too short we could get in a situation
where the self refresh exits are taking so long we queue up a self refresh
entry before the exit commit is even finished.

This patch changes the idle timeout to a moving average of the entry
times + a moving average of exit times + the crtc constant.

This patch was tested on rockchip, with a kevin CrOS panel the idle
delay averages out to about ~235ms (35 entry + 100 exit + 100 const). On
the same board, the bob panel idle delay lands around ~340ms (90 entry
+ 150 exit + 100 const).

WRT the dedicated mutex in self_refresh_data, it would be nice if we
could rely on drm_crtc.mutex to protect the average times, but there are
a few reasons why a separate lock is a better choice:
- We can't rely on drm_crtc.mutex being held if we're doing a nonblocking
  commit
- We can't grab drm_crtc.mutex since drm_modeset_lock() doesn't tell us
  whether the lock was already held in the acquire context (it eats
  -EALREADY), so we can't tell if we should drop it or not
- We don't need such a heavy-handed lock for what we're trying to do,
  commit ordering doesn't matter, so a point-of-use lock will be less
  contentious

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link to v1: https://patchwork.freedesktop.org/patch/msgid/20190917200443.64481-2-sean@poorly.run
Link: https://patchwork.freedesktop.org/patch/msgid/20190918200734.149876-2-sean@poorly.run
Changes in v2:
- Migrate locking explanation from comment to commit msg (Daniel)
- Turf constant entry delay and multiply the avg times by 2 (Daniel)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 3a67f63c3146abfbe50b89c7d442335469ff8436..3ef2ac52ce942c303fbec865587fa7b95933ad15 100644 (file)
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -26,6 +26,7 @@
  */
 
 #include <linux/dma-fence.h>
+#include <linux/ktime.h>
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
@@ -1580,9 +1581,23 @@ static void commit_tail(struct drm_atomic_state *old_state)
 {
        struct drm_device *dev = old_state->dev;
        const struct drm_mode_config_helper_funcs *funcs;
+       ktime_t start;
+       s64 commit_time_ms;
 
        funcs = dev->mode_config.helper_private;
 
+       /*
+        * We're measuring the _entire_ commit, so the time will vary depending
+        * on how many fences and objects are involved. For the purposes of self
+        * refresh, this is desirable since it'll give us an idea of how
+        * congested things are. This will inform our decision on how often we
+        * should enter self refresh after idle.
+        *
+        * These times will be averaged out in the self refresh helpers to avoid
+        * overreacting over one outlier frame
+        */
+       start = ktime_get();
+
        drm_atomic_helper_wait_for_fences(dev, old_state, false);
 
        drm_atomic_helper_wait_for_dependencies(old_state);
@@ -1592,6 +1607,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
        else
                drm_atomic_helper_commit_tail(old_state);
 
+       commit_time_ms = ktime_ms_delta(ktime_get(), start);
+       if (commit_time_ms > 0)
+               drm_self_refresh_helper_update_avg_times(old_state,
+                                                (unsigned long)commit_time_ms);
+
        drm_atomic_helper_commit_cleanup_done(old_state);
 
        drm_atomic_state_put(old_state);

diff --git a/drivers/gpu/drm/drm_self_refresh_helper.c b/drivers/gpu/drm/drm_self_refresh_helper.c
index 9095cebf21474d48cbc8a46f646d0784c89ff32a..68f4765a5896472775500836b7dfc537de0b862a 100644 (file)
--- a/drivers/gpu/drm/drm_self_refresh_helper.c
+++ b/drivers/gpu/drm/drm_self_refresh_helper.c
@@ -5,6 +5,7 @@
  * Authors:
  * Sean Paul <seanpaul@chromium.org>
  */
+#include <linux/average.h>
 #include <linux/bitops.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
@@ -50,10 +51,17 @@
  * atomic_check when &drm_crtc_state.self_refresh_active is true.
  */
 
+#define SELF_REFRESH_AVG_SEED_MS 200
+
+DECLARE_EWMA(psr_time, 4, 4)
+
 struct drm_self_refresh_data {
        struct drm_crtc *crtc;
        struct delayed_work entry_work;
-       unsigned int entry_delay_ms;
+
+       struct mutex avg_mutex;
+       struct ewma_psr_time entry_avg_ms;
+       struct ewma_psr_time exit_avg_ms;
 };
 
 static void drm_self_refresh_helper_entry_work(struct work_struct *work)
@@ -121,6 +129,44 @@ out_drop_locks:
        drm_modeset_acquire_fini(&ctx);
 }
 
+/**
+ * drm_self_refresh_helper_update_avg_times - Updates a crtc's SR time averages
+ * @state: the state which has just been applied to hardware
+ * @commit_time_ms: the amount of time in ms that this commit took to complete
+ *
+ * Called after &drm_mode_config_funcs.atomic_commit_tail, this function will
+ * update the average entry/exit self refresh times on self refresh transitions.
+ * These averages will be used when calculating how long to delay before
+ * entering self refresh mode after activity.
+ */
+void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
+                                             unsigned int commit_time_ms)
+{
+       struct drm_crtc *crtc;
+       struct drm_crtc_state *old_crtc_state, *new_crtc_state;
+       int i;
+
+       for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state,
+                                     new_crtc_state, i) {
+               struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
+               struct ewma_psr_time *time;
+
+               if (old_crtc_state->self_refresh_active ==
+                   new_crtc_state->self_refresh_active)
+                       continue;
+
+               if (new_crtc_state->self_refresh_active)
+                       time = &sr_data->entry_avg_ms;
+               else
+                       time = &sr_data->exit_avg_ms;
+
+               mutex_lock(&sr_data->avg_mutex);
+               ewma_psr_time_add(time, commit_time_ms);
+               mutex_unlock(&sr_data->avg_mutex);
+       }
+}
+EXPORT_SYMBOL(drm_self_refresh_helper_update_avg_times);
+
 /**
  * drm_self_refresh_helper_alter_state - Alters the atomic state for SR exit
  * @state: the state currently being checked
@@ -152,6 +198,7 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
 
        for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
                struct drm_self_refresh_data *sr_data;
+               unsigned int delay;
 
                /* Don't trigger the entry timer when we're already in SR */
                if (crtc_state->self_refresh_active)
@@ -161,8 +208,13 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
                if (!sr_data)
                        continue;
 
+               mutex_lock(&sr_data->avg_mutex);
+               delay = (ewma_psr_time_read(&sr_data->entry_avg_ms) +
+                        ewma_psr_time_read(&sr_data->exit_avg_ms)) * 2;
+               mutex_unlock(&sr_data->avg_mutex);
+
                mod_delayed_work(system_wq, &sr_data->entry_work,
-                                msecs_to_jiffies(sr_data->entry_delay_ms));
+                                msecs_to_jiffies(delay));
        }
 }
 EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
@@ -170,12 +222,10 @@ EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
 /**
  * drm_self_refresh_helper_init - Initializes self refresh helpers for a crtc
  * @crtc: the crtc which supports self refresh supported displays
- * @entry_delay_ms: amount of inactivity to wait before entering self refresh
  *
  * Returns zero if successful or -errno on failure
  */
-int drm_self_refresh_helper_init(struct drm_crtc *crtc,
-                                unsigned int entry_delay_ms)
+int drm_self_refresh_helper_init(struct drm_crtc *crtc)
 {
        struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
 
@@ -189,8 +239,18 @@ int drm_self_refresh_helper_init(struct drm_crtc *crtc,
 
        INIT_DELAYED_WORK(&sr_data->entry_work,
                          drm_self_refresh_helper_entry_work);
-       sr_data->entry_delay_ms = entry_delay_ms;
        sr_data->crtc = crtc;
+       mutex_init(&sr_data->avg_mutex);
+       ewma_psr_time_init(&sr_data->entry_avg_ms);
+       ewma_psr_time_init(&sr_data->exit_avg_ms);
+
+       /*
+        * Seed the averages so they're non-zero (and sufficiently large
+        * for even poorly performing panels). As time goes on, this will be
+        * averaged out and the values will trend to their true value.
+        */
+       ewma_psr_time_add(&sr_data->entry_avg_ms, SELF_REFRESH_AVG_SEED_MS);
+       ewma_psr_time_add(&sr_data->exit_avg_ms, SELF_REFRESH_AVG_SEED_MS);
 
        crtc->self_refresh_data = sr_data;
        return 0;

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index 2f821c58007cfe8a62ed805306f980d3577121cb..613404f86668d24667718ddb48bbb20ad73ab09f 100644 (file)
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -39,8 +39,6 @@
 #include "rockchip_drm_vop.h"
 #include "rockchip_rgb.h"
 
-#define VOP_SELF_REFRESH_ENTRY_DELAY_MS 100
-
 #define VOP_WIN_SET(vop, win, name, v) \
                vop_reg_set(vop, &win->phy->name, win->base, ~0, v, #name)
 #define VOP_SCL_SET(vop, win, name, v) \
@@ -1563,8 +1561,7 @@ static int vop_create_crtc(struct vop *vop)
        init_completion(&vop->line_flag_completion);
        crtc->port = port;
 
-       ret = drm_self_refresh_helper_init(crtc,
-                                          VOP_SELF_REFRESH_ENTRY_DELAY_MS);
+       ret = drm_self_refresh_helper_init(crtc);
        if (ret)
                DRM_DEV_DEBUG_KMS(vop->dev,
                        "Failed to init %s with SR helpers %d, ignoring\n",

diff --git a/include/drm/drm_self_refresh_helper.h b/include/drm/drm_self_refresh_helper.h
index 397a583ccca7ebd68d8f00ebb43a88662c1f1161..5b79d253fb46e80e0319e16f5eb9d2edbb74b1f6 100644 (file)
--- a/include/drm/drm_self_refresh_helper.h
+++ b/include/drm/drm_self_refresh_helper.h
@@ -12,9 +12,9 @@ struct drm_atomic_state;
 struct drm_crtc;
 
 void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state);
+void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
+                                             unsigned int commit_time_ms);
 
-int drm_self_refresh_helper_init(struct drm_crtc *crtc,
-                                unsigned int entry_delay_ms);
-
+int drm_self_refresh_helper_init(struct drm_crtc *crtc);
 void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc);
 #endif