• Daniel Vetter's avatar
    drm/i915: fixup seqno allocation logic for lazy_request · 53d227f2
    Daniel Vetter authored
    Currently we reserve seqnos only when we emit the request to the ring
    (by bumping dev_priv->next_seqno), but start using it much earlier for
    ring->oustanding_lazy_request. When 2 threads compete for the gpu and
    run on two different rings (e.g. ddx on blitter vs. compositor)
    hilarity ensued, especially when we get constantly interrupted while
    reserving buffers.
    
    Breakage seems to have been introduced in
    
    commit 6f392d54
    Author: Chris Wilson <chris@chris-wilson.co.uk>
    Date:   Sat Aug 7 11:01:22 2010 +0100
    
        drm/i915: Use a common seqno for all rings.
    
    This patch fixes up the seqno reservation logic by moving it into
    i915_gem_next_request_seqno. The ring->add_request functions now
    superflously still return the new seqno through a pointer, that will
    be refactored in the next patch.
    
    Note that with this change we now unconditionally allocate a seqno,
    even when ->add_request might fail because the rings are full and the
    gpu died. But this does not open up a new can of worms because we can
    already leave behind an outstanding_request_seqno if e.g. the caller
    gets interrupted with a signal while stalling for the gpu in the
    eviciton paths. And with the bugfix we only ever have one seqno
    allocated per ring (and only that ring), so there are no ordering
    issues with multiple outstanding seqnos on the same ring.
    
    v2: Keep i915_gem_get_seqno (but move it to i915_gem.c) to make it
    clear that we only have one seqno counter for all rings. Suggested by
    Chris Wilson.
    
    v3: As suggested by Chris Wilson use i915_gem_next_request_seqno
    instead of ring->oustanding_lazy_request to make the follow-up
    refactoring more clearly correct. Also improve the commit message
    with issues discussed on irc.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45181
    Tested-by: Nicolas Kalkhof nkalkhof()at()web.de
    Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Signed-Off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    53d227f2
intel_ringbuffer.c 36.8 KB