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iris: Tune the BO cache's bucket sizes

Kenneth Graunke requested to merge kwg/mesa:iris-tune-buckets into main

(this patch was supposed to land as part of !25447 (merged) but somehow I botched it and dropped it during rebases and addressing review feedback) :(

With the introduction of the slab allocator, most of our small allocations now hit that rather than directly hitting the bucket cache. Those now show up as 2MB slab allocations from the cache's perspective. So, we don't need quite as many buckets. (Note that only allocations in IRIS_MEMZONE_OTHER are suballocated today.)

Previously, we had 55 buckets, going from 4KB to 112MB, with sizes N, N+1/4, N+1/2, N+3/4 for a series of power-of-two N's.

This patch prunes it down to 25 buckets:

  • 4K-4MB => power-of-two sizes only
  • 6MB => a one-off bucket to reduce waste between 4MB and 8MB
  • 8MB+ => the usual N, N+1/4, N+1/2, N+3/4 system
  • 64MB => the largest bucket size

In particular, this eliminates the 1.75MB, 2.5MB, 3MB, 3.5MB, and 7MB buckets in favor of multiples of 2MB. Allocating multiples of 2MB is preferable because it allows the kernel to allocate 64KB pages rather than being stuck using inefficient 4K pages. And, the amount of waste from bumping to the next multiple of 2MB isn't huge in that range of sizes. We also eliminate buckets larger than 64MB because they're rarely used, and also the amount of waste from rounding up to the 80/96/112MB buckets can get pretty large.

Reviewed-by: José Roberto de Souza jose.souza@intel.com Fixes: 0b6693a3 ("iris: Align fresh BO allocations to 2MB in size") Closes: #10219 (closed)

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