• Chris Wilson's avatar
    drm/i915: Preallocate next seqno before touching the ring · 9d773091
    Chris Wilson authored
    Based on the work by Mika Kuoppala, we realised that we need to handle
    seqno wraparound prior to committing our changes to the ring. The most
    obvious point then is to grab the seqno inside intel_ring_begin(), and
    then to reuse that seqno for all ring operations until the next request.
    As intel_ring_begin() can fail, the callers must already be prepared to
    handle such failure and so we can safely add further checks.
    
    This patch looks like it should be split up into the interface
    changes and the tweaks to move seqno wrapping from the execbuffer into
    the core seqno increment. However, I found no easy way to break it into
    incremental steps without introducing further broken behaviour.
    
    v2: Mika found a silly mistake and a subtle error in the existing code;
    inside i915_gem_retire_requests() we were resetting the sync_seqno of
    the target ring based on the seqno from this ring - which are only
    related by the order of their allocation, not retirement. Hence we were
    applying the optimisation that the rings were synchronised too early,
    fortunately the only real casualty there is the handling of seqno
    wrapping.
    
    v3: Do not forget to reset the sync_seqno upon module reinitialisation,
    ala resume.
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Cc: Mika Kuoppala <mika.kuoppala@intel.com>
    Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=863861
    Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> [v2]
    Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    9d773091
i915_drv.h 53 KB