drm/i915: Eliminate lots of iterations over the execobjects array
The major scaling bottleneck in execbuffer is the processing of the execobjects. Creating an auxiliary list is inefficient when compared to using the execobject array we already have allocated. Reservation is then split into phases. As we lookup up the VMA, we try and bind it back into active location. Only if that fails, do we add it to the unbound list for phase 2. In phase 2, we try and add all those objects that could not fit into their previous location, with fallback to retrying all objects and evicting the VM in case of severe fragmentation. (This is the same as before, except that phase 1 is now done inline with looking up the VMA to avoid an iteration over the execobject array. In the ideal case, we eliminate the separate reservation phase). During the reservation phase, we only evict from the VM between passes (rather than currently as we try to fit every new VMA). In testing with Unreal Engine's Atlantis demo which stresses the eviction logic on gen7 class hardware, this speed up the framerate by a factor of 2. The second loop amalgamation is between move_to_gpu and move_to_active. As we always submit the request, even if incomplete, we can use the current request to track active VMA as we perform the flushes and synchronisation required. The next big advancement is to avoid copying back to the user any execobjects and relocations that are not changed. v2: Add a Theory of Operation spiel. v3: Fall back to slow relocations in preparation for flushing userptrs. v4: Document struct members, factor out eb_validate_vma(), add a few more comments to explain some magic and hide other magic behind macros. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
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