[Intel-gfx] [PATCH 0/3] New DDB allocation algorithm

[Matt Roper]

Our current algorithm for partitioning a pipe's DDB allocation bases
plane allocations exclusively on the proportion of the pipe's data rate
that the plane contributes.  This is a simple heuristic that works
pretty well in a lot of cases, but it breaks down when there's a large
difference in plane sizes (e.g., one full-screen plane and another
100x100 plane).  When sizes are very different, using proportional data
rate can leave the smaller planes without enough DDB allocation to even
hit their level 0 watermarks (which means the whole configuration
becomes impossible), or can artificially limit how high of a watermark
level the smaller planes can achieve.  These problems are most visible
on APL (due to the platform's smaller DDB in general).

A better algorithm is to calculate watermarks first, DDB second, and use
the block counts from the watermark calculation to give planes exactly
the allocation they need to hit the highest possible global watermark
level.  Mahesh took a stab at implementing this algorithm about 1.5
years ago, but there were some bugs that led to regressions and nobody
had time to track them down.  Our watermark code has evolved
significantly since that time, but the problems with the original
datarate-proportional algorithm remain.

Matt Roper (3):
  drm/i915: Remove a very stale FIXME
  drm/i915: Don't use DDB allocation when choosing gen9 watermark method
  drm/i915: Switch to level-based DDB allocation algorithm

 drivers/gpu/drm/i915/intel_pm.c | 356 ++++++++++++++--------------------------
 1 file changed, 121 insertions(+), 235 deletions(-)

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