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author | Sean Paul <seanpaul@chromium.org> | 2019-09-18 16:07:29 -0400 |
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committer | Sean Paul <seanpaul@chromium.org> | 2019-09-19 10:03:32 -0400 |
commit | d4da4e33341c5e6159543acc03559cb24f520bc2 (patch) | |
tree | 4fe613cff902325c07fd4e9706d7dcfc5035f115 /drivers/gpu/drm/drm_atomic_helper.c | |
parent | 2d2e0b90a08f1e3a47b3ee852b27c219295423ef (diff) | |
download | linux-d4da4e33341c5e6159543acc03559cb24f520bc2.tar.bz2 |
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.c | 20 |
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); |