• Chris Wilson's avatar
    drm/i915: Replace obj->pin_global with obj->frontbuffer · 5a90606d
    Chris Wilson authored
    
    
    obj->pin_global was originally used as a means to keep the shrinker off
    the active scanout, but we use the vma->pin_count itself for that and
    the obj->frontbuffer to delay shrinking active framebuffers. The other
    role that obj->pin_global gained was for spotting display objects inside
    GEM and working harder to keep those coherent; for which we can again
    simply inspect obj->frontbuffer directly.
    
    Coming up next, we will want to manipulate the pin_global counter
    outside of the principle locks, so would need to make pin_global atomic.
    However, since obj->frontbuffer is already managed atomically, it makes
    sense to use that the primary key for display objects instead of having
    pin_global.
    
    Ville pointed out the principle difference is that obj->frontbuffer is
    set for as long as an intel_framebuffer is attached to an object, but
    obj->pin_global was only raised for as long as the object was active. In
    practice, this means that we consider the object as being on the scanout
    for longer than is strictly required, causing us to be more proactive in
    flushing -- though it should be true that we would have flushed
    eventually when the back became the front, except that on the flip path
    that flush is async but when hit from another ioctl it will be
    synchronous.
    
    v2: i915_gem_object_is_framebuffer()
    
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
    Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20190902040303.14195-5-chris@chris-wilson.co.uk
    5a90606d