[PATCH 2/2] drm: Measure Self Refresh Entry/Exit times to avoid thrashing
Sean Paul
sean at poorly.run
Tue Sep 17 20:04:33 UTC 2019
From: Sean Paul <seanpaul at 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 at 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 at 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);
--
Sean Paul, Software Engineer, Google / Chromium OS
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