Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Medium] Factual error in documentation and commit message regarding __force_merge() execution path --
--- Patch [2]: [PATCH v8 2/2] gpu/tests/buddy: add dirty tracker performance KUnit test --- commit fc0bf373f19d84c8ba58395148cb3dec974d2a81 Author: Arunpravin Paneer Selvam <[email protected]> gpu/tests/buddy: add dirty tracker performance KUnit test This commit adds a KUnit test to demonstrate the performance advantage of the decoupled dirty-tracker design over the older dual-tree force_merge approach during severe fragmentation scenarios. > 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 [Severity: Medium] Is this description accurate regarding the execution of __force_merge()? Looking at gpu_buddy_alloc_blocks(), when start is 0, size is SZ_4G, and end is SZ_4G, the condition start + size == end evaluates to true: /* Actual range allocation */ if (start + size == end) { if (!IS_ALIGNED(start | end, min_block_size)) return -EINVAL; return __gpu_buddy_alloc_range(mm, start, size, flags, NULL, blocks); } This takes the __gpu_buddy_alloc_range() fast-path, which completely bypasses __alloc_contig_try_harder() and never invokes __force_merge(). Does the 71 ms latency actually come from the O(N) overhead of traversing and linking the 1,048,576 unmerged 4 KiB blocks covering the range, rather than the cost of __force_merge()? > diff --git a/drivers/gpu/tests/gpu_buddy_test.c > b/drivers/gpu/tests/gpu_buddy_test.c > index 198d8dc4e3f0e..4dc54ed33269e 100644 > --- a/drivers/gpu/tests/gpu_buddy_test.c > +++ b/drivers/gpu/tests/gpu_buddy_test.c [ ... ] > @@ -283,6 +283,119 @@ static void > gpu_test_buddy_fragmentation_performance(struct kunit *test) [ ... ] > +static void gpu_test_buddy_dirty_tracker_performance(struct kunit *test) > +{ [ ... ] > + /* > + * 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 [Severity: Medium] The same documentation mismatch appears here in the inline comment for gpu_test_buddy_dirty_tracker_performance(). Since this 4 GiB allocation triggers the exact range allocation path in gpu_buddy_alloc_blocks(), __force_merge() is not invoked. Could we update the comment to accurately reflect the source of the latency in the old design? > + * 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"); -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=2
