Add gpu_test_buddy_dirty_tracker_performance to demonstrate the key
advantage of the decoupled dirty-tracker design over the old dual-tree
/ force_merge approach.
The test runs two scenarios on a 4 GiB pool after alternating
clear/dirty fragmentation at 4 KiB granularity:
1. Contiguous 4 GiB alloc: the old design requires __force_merge()
to rebuild max_order from scratch; the new design coalesces during
free() so the alloc is O(log N).
old (force_merge) - 71 ms
dirty tracker design - 17 ms
2. Repeated 256 KiB alloc throughput: the old design pays
__force_merge() on every alloc; the new design does not.
old (force_merge) - 95 ms
dirty tracker design - 24 ms
Assisted-by: Claude:claude-opus-4-8
Cc: Matthew Auld <[email protected]>
Cc: Christian König <[email protected]>
Signed-off-by: Arunpravin Paneer Selvam <[email protected]>
---
drivers/gpu/tests/gpu_buddy_test.c | 110 +++++++++++++++++++++++++++++
1 file changed, 110 insertions(+)
diff --git a/drivers/gpu/tests/gpu_buddy_test.c
b/drivers/gpu/tests/gpu_buddy_test.c
index e31f368ada95..e37505849ecc 100644
--- a/drivers/gpu/tests/gpu_buddy_test.c
+++ b/drivers/gpu/tests/gpu_buddy_test.c
@@ -283,6 +283,115 @@ static void
gpu_test_buddy_fragmentation_performance(struct kunit *test)
gpu_buddy_fini(&mm);
}
+static void gpu_test_buddy_dirty_tracker_performance(struct kunit *test)
+{
+ struct gpu_buddy_block *block, *tmp;
+ unsigned long elapsed_ms;
+ LIST_HEAD(clear_blocks);
+ LIST_HEAD(dirty_blocks);
+ LIST_HEAD(allocated);
+ struct gpu_buddy mm;
+ LIST_HEAD(results);
+ ktime_t start, end;
+ int i, count;
+
+ /*
+ * Contiguous alloc latency after alternating clear/dirty fragmentation
+ *
+ * Fill a 4 GiB pool with 4 KiB allocations, partition them into
+ * alternating cleared and dirty sets, then free both. In the old
+ * dual-tree design every adjacent buddy pair has one cleared half and
+ * one dirty half, so the pair sits on opposite sides of the clear/dirty
+ * merge barrier and cannot be coalesced at free() time. The pool
+ * stays fully fragmented and the subsequent contiguous 4 GiB allocation
+ * has to invoke __force_merge() to climb back up to max_order before
+ * it can succeed. With the dirty-tracker design buddy pairs coalesce
+ * unconditionally during free(), so the pool is already at max_order
+ * before the timed alloc begins and __force_merge() is not needed.
+ */
+ KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_init(&mm, SZ_4G, SZ_4K),
+ "buddy_init failed\n");
+
+ for (i = 0; i < SZ_4G / SZ_4K; i++)
+ KUNIT_ASSERT_FALSE_MSG(test,
+ gpu_buddy_alloc_blocks(&mm, 0, SZ_4G,
SZ_4K, SZ_4K,
+ &allocated, 0),
+ "buddy_alloc hit an error size=%u\n",
SZ_4K);
+
+ count = 0;
+ list_for_each_entry_safe(block, tmp, &allocated, link) {
+ if (count++ % 2 == 0)
+ list_move_tail(&block->link, &clear_blocks);
+ else
+ list_move_tail(&block->link, &dirty_blocks);
+ }
+
+ gpu_buddy_free_list(&mm, &clear_blocks, GPU_BUDDY_CLEARED);
+ gpu_buddy_free_list(&mm, &dirty_blocks, 0);
+
+ start = ktime_get();
+ KUNIT_ASSERT_FALSE_MSG(test,
+ gpu_buddy_alloc_blocks(&mm, 0, SZ_4G, SZ_4G,
SZ_4K,
+ &results,
+
GPU_BUDDY_CONTIGUOUS_ALLOCATION),
+ "contiguous alloc failed\n");
+ end = ktime_get();
+ elapsed_ms = ktime_to_ms(ktime_sub(end, start));
+
+ kunit_info(test, "Contiguous alloc after fragmentation: %lu ms\n",
+ elapsed_ms);
+
+ gpu_buddy_free_list(&mm, &results, 0);
+ gpu_buddy_fini(&mm);
+
+ /*
+ * Repeated alloc throughput from a maximally fragmented pool
+ *
+ * Fill a 4 GiB pool with 4 KiB allocations, free even-indexed blocks
+ * as cleared and odd-indexed blocks as dirty. The alternating pattern
+ * ensures every adjacent buddy pair has one cleared half and one dirty
+ * half, so each pair lands on opposite sides of the old merge barrier.
+ * Each of the 16 384 x 256 KiB allocations in the timed loop has to
+ * pay the __force_merge() cost on the alloc path under the old design.
+ * With the dirty-tracker design the pool collapses to one max_order
+ * block during free(), so each alloc is a simple O(log N) split.
+ */
+ KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_init(&mm, SZ_4G, SZ_4K),
+ "buddy_init failed\n");
+
+ for (i = 0; i < SZ_4G / SZ_4K; i++)
+ KUNIT_ASSERT_FALSE_MSG(test,
+ gpu_buddy_alloc_blocks(&mm, 0, SZ_4G,
SZ_4K, SZ_4K,
+ &allocated, 0),
+ "buddy_alloc hit an error size=%u\n",
SZ_4K);
+
+ count = 0;
+ list_for_each_entry_safe(block, tmp, &allocated, link) {
+ if (count++ % 2 == 0)
+ list_move_tail(&block->link, &clear_blocks);
+ else
+ list_move_tail(&block->link, &dirty_blocks);
+ }
+
+ gpu_buddy_free_list(&mm, &clear_blocks, GPU_BUDDY_CLEARED);
+ gpu_buddy_free_list(&mm, &dirty_blocks, 0);
+
+ start = ktime_get();
+ for (i = 0; i < SZ_4G / SZ_256K; i++)
+ KUNIT_ASSERT_FALSE_MSG(test,
+ gpu_buddy_alloc_blocks(&mm, 0, SZ_4G,
SZ_256K, SZ_4K,
+ &results, 0),
+ "buddy_alloc hit an error size=%u\n",
SZ_256K);
+ end = ktime_get();
+ elapsed_ms = ktime_to_ms(ktime_sub(end, start));
+
+ kunit_info(test, "Repeated 256 KiB allocs from fragmented pool: %lu
ms\n",
+ elapsed_ms);
+
+ gpu_buddy_free_list(&mm, &results, 0);
+ gpu_buddy_fini(&mm);
+}
+
static void gpu_test_buddy_alloc_range_bias(struct kunit *test)
{
u32 mm_size, size, ps, bias_size, bias_start, bias_end, bias_rem;
@@ -1396,6 +1505,7 @@ static struct kunit_case gpu_buddy_tests[] = {
KUNIT_CASE(gpu_test_buddy_alloc_range),
KUNIT_CASE(gpu_test_buddy_alloc_range_bias),
KUNIT_CASE_SLOW(gpu_test_buddy_fragmentation_performance),
+ KUNIT_CASE_SLOW(gpu_test_buddy_dirty_tracker_performance),
KUNIT_CASE(gpu_test_buddy_alloc_exceeds_max_order),
KUNIT_CASE(gpu_test_buddy_offset_aligned_allocation),
KUNIT_CASE(gpu_test_buddy_subtree_offset_alignment_stress),
--
2.34.1
