src/panfrost/shared/pan_minmax_cache.c

   1 /*
   2  * Copyright (c) 2020 Collabora, Ltd.
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  20  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  21  * SOFTWARE.
  22  *
  23  * Authors (Collabora):
  24  *   Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
  25  */
  26
  27 /* Index buffer min/max cache. We need to calculate the min/max for arbitrary
  28  * slices (start, start + count) of the index buffer at drawtime. As this can
  29  * be quite expensive, we cache. Conceptually, we just use a hash table mapping
  30  * the key (start, count) to the value (min, max). In practice, mesa's hash
  31  * table implementation is higher overhead than we would like and makes
  32  * handling memory usage a little complicated. So we use this data structure
  33  * instead. Searching is O(n) to the size, but the size is capped at the
  34  * PANFROST_MINMAX_SIZE constant (so this is a tradeoff between cache hit/miss
  35  * ratio and cache search speed). Note that keys are adjacent so we get cache
  36  * line alignment benefits. Insertion is O(1) and in-order until the cache
  37  * fills up, after that it evicts the oldest cached value in a ring facilitated
  38  * by index.
  39  */
  40
  41 #include "pan_minmax_cache.h"
  42
  43 bool
  44 panfrost_minmax_cache_get(struct panfrost_minmax_cache *cache, unsigned start, unsigned count,
  45                      unsigned *min_index, unsigned *max_index)
  46 {
  47         uint64_t ht_key = (((uint64_t)count) << 32) | start;
  48         bool found = false;
  49
  50         if (!cache)
  51            return false;
  52
  53         for (unsigned i = 0; i < cache->size; ++i) {
  54                 if (cache->keys[i] == ht_key) {
  55                         uint64_t hit = cache->values[i];
  56
  57                         *min_index = hit & 0xffffffff;
  58                         *max_index = hit >> 32;
  59                         found = true;
  60                         break;
  61                 }
  62         }
  63
  64         return found;
  65 }
  66
  67 void
  68 panfrost_minmax_cache_add(struct panfrost_minmax_cache *cache, unsigned start, unsigned count,
  69                      unsigned min_index, unsigned max_index)
  70 {
  71         uint64_t ht_key = (((uint64_t)count) << 32) | start;
  72         uint64_t value = min_index | (((uint64_t)max_index) << 32);
  73         unsigned index = 0;
  74
  75         if (!cache)
  76                 return;
  77
  78         if (cache->size == PANFROST_MINMAX_SIZE) {
  79                 index = cache->index++;
  80                 cache->index = cache->index % PANFROST_MINMAX_SIZE;
  81         } else {
  82                 index = cache->size++;
  83         }
  84
  85         cache->keys[index] =  ht_key;
  86         cache->values[index] = value;
  87
  88 }
  89
  90 /* If we've been caching min/max indices and we update the index
  91  * buffer, that may invalidate the min/max. Check what's been cached vs
  92  * what we've written, and throw out invalid entries. */
  93
  94 void
  95 panfrost_minmax_cache_invalidate(struct panfrost_minmax_cache *cache, struct pipe_transfer *transfer)
  96 {
  97         /* Ensure there is a cache to invalidate and a write */
  98         if (!cache)
  99                 return;
 100
 101         if (!(transfer->usage & PIPE_TRANSFER_WRITE))
 102                 return;
 103
 104         unsigned valid_count = 0;
 105
 106         for (unsigned i = 0; i < cache->size; ++i) {
 107                 uint64_t key = cache->keys[i];
 108
 109                 uint32_t start = key & 0xffffffff;
 110                 uint32_t count = key >> 32;
 111
 112                 /* 1D range intersection */
 113                 bool invalid = MAX2(transfer->box.x, start) < MIN2(transfer->box.x + transfer->box.width, start + count);
 114                 if (!invalid) {
 115                         cache->keys[valid_count] = key;
 116                         cache->values[valid_count] = cache->values[i];
 117                         valid_count++;
 118                 }
 119         }
 120
 121         cache->size = valid_count;
 122         cache->index = 0;
 123 }