• Sean Paul's avatar
    drm: Measure Self Refresh Entry/Exit times to avoid thrashing · d4da4e33
    Sean Paul authored
    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: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: default avatarSean 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)
    d4da4e33
drm_self_refresh_helper.h 559 Bytes