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authorSean Paul <seanpaul@chromium.org>2019-09-18 23:07:29 +0300
committerSean Paul <seanpaul@chromium.org>2019-09-19 17:03:32 +0300
commitd4da4e33341c5e6159543acc03559cb24f520bc2 (patch)
tree4fe613cff902325c07fd4e9706d7dcfc5035f115 /drivers/gpu/drm/drm_atomic_helper.c
parent2d2e0b90a08f1e3a47b3ee852b27c219295423ef (diff)
downloadlinux-d4da4e33341c5e6159543acc03559cb24f520bc2.tar.xz
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)
Diffstat (limited to 'drivers/gpu/drm/drm_atomic_helper.c')
-rw-r--r--drivers/gpu/drm/drm_atomic_helper.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 3a67f63c3146..3ef2ac52ce94 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>
@@ -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);