From: Sean Paul seanpaul@chromium.org

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).

Signed-off-by: Sean Paul seanpaul@chromium.org --- drivers/gpu/drm/drm_atomic_helper.c | 20 +++++++ drivers/gpu/drm/drm_self_refresh_helper.c | 71 ++++++++++++++++++++++- include/drm/drm_self_refresh_helper.h | 2 + 3 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 9d7e4da6c292..3f13fa9a9e24 100644 --- 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> @@ -1570,9 +1571,23 @@ 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); @@ -1582,6 +1597,11 @@ 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 9095cebf2147..522430f8eef1 100644 --- 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 +51,16 @@ * atomic_check when &drm_crtc_state.self_refresh_active is true. */

+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 +128,59 @@ static void drm_self_refresh_helper_entry_work(struct work_struct *work) 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; + + /* + * It might be nice if we could rely on &drm_crtc.mutex to + * protect &drm_self_refresh_data.exit_avg_ms, as we do with + * &drm_self_refresh_data.entry_avg_ms, but there are a few + * reasons why a separate lock is a better choice: + * - We can't rely on &drm_crtc.mutex being held here if we're + * doing a nonblocking commit + * - We can't grab &drm_crtc.mutex here 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 here, commit ordering doesn't matter, so a + * point-of-use lock will be less contentious + */ + 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 +212,7 @@ 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 +222,13 @@ 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) + + sr_data->entry_delay_ms; + 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); @@ -191,6 +257,9 @@ int drm_self_refresh_helper_init(struct drm_crtc *crtc, 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);

crtc->self_refresh_data = sr_data; return 0; diff --git a/include/drm/drm_self_refresh_helper.h b/include/drm/drm_self_refresh_helper.h index 397a583ccca7..ff777690c564 100644 --- a/include/drm/drm_self_refresh_helper.h +++ b/include/drm/drm_self_refresh_helper.h @@ -12,6 +12,8 @@ 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);

On Tue, Sep 17, 2019 at 04:04:32PM -0400, Sean Paul wrote:

From: Sean Paul seanpaul@chromium.org

Artifacts of previous revisions.

Signed-off-by: Sean Paul seanpaul@chromium.org

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

---

drivers/gpu/drm/drm_self_refresh_helper.c | 1 - include/drm/drm_crtc.h | 2 +- 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_self_refresh_helper.c b/drivers/gpu/drm/drm_self_refresh_helper.c index 4b9424a8f1f1..9095cebf2147 100644 --- a/drivers/gpu/drm/drm_self_refresh_helper.c +++ b/drivers/gpu/drm/drm_self_refresh_helper.c @@ -53,7 +53,6 @@ struct drm_self_refresh_data { struct drm_crtc *crtc; struct delayed_work entry_work;

• struct drm_atomic_state *save_state; unsigned int entry_delay_ms;

};

diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index 7e2963cad543..742b31043898 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -1107,7 +1107,7 @@ struct drm_crtc { /** * @self_refresh_data: Holds the state for the self refresh helpers *

• * Initialized via drm_self_refresh_helper_register().
  

• * Initialized via drm_self_refresh_helper_init().
  

  */ struct drm_self_refresh_data *self_refresh_data;

};

Sean Paul, Software Engineer, Google / Chromium OS