[PATCH v3 1/2] dma-fence: Add unwrap mode enum and macro for in-place deduplication
Arvind Yadav
Arvind.Yadav at amd.com
Tue Apr 29 15:24:47 UTC 2025
Introduce a new `enum dma_fence_unwrap_mode` to support multiple modes
of fence unwrapping and merging behavior. This lays the groundwork for
more flexible and efficient fence operations.
Add a new macro `dma_fence_unwrap_shrink_array()` to allow callers to
unwrap, deduplicate, and sort dma_fence arrays in-place, avoiding
additional memory allocations. This mode filters out already signaled
fences and keeps only the latest fence per context.
To support this, refactor `__dma_fence_unwrap_merge()` to handle both
merge and shrink modes through the new `dma_fence_unwrap_mode` parameter.
The sorting and deduplication logic is extracted into a new helper function
`dma_fence_unwrap_dedup_sort()`.
These changes allow clients to efficiently compact arrays of fences with
minimal overhead, improving memory usage and performance in common
scenarios like command submission or dependency tracking.
v2: - Export this code from dma-fence-unwrap.c(by Christian).
v3: - To split this in a dma_buf patch and amd userq patch(by Sunil).
- No need to add a new function just re-use existing(by Christian).
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Christian Koenig <christian.koenig at amd.com>
Cc: Sunil Khatri <sunil.khatri at amd.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
Signed-off-by: Arvind Yadav <Arvind.Yadav at amd.com>
---
drivers/dma-buf/dma-fence-unwrap.c | 54 +++++++++++++++++++++---------
include/linux/dma-fence-unwrap.h | 44 ++++++++++++++++++++++--
2 files changed, 81 insertions(+), 17 deletions(-)
diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
index 2a059ac0ed27..f389c37a0eb5 100644
--- a/drivers/dma-buf/dma-fence-unwrap.c
+++ b/drivers/dma-buf/dma-fence-unwrap.c
@@ -79,15 +79,51 @@ static int fence_cmp(const void *_a, const void *_b)
return 0;
}
+static void dma_fence_unwrap_dedup_sort(struct dma_fence **array,
+ unsigned int *count)
+{
+ int i, j;
+
+ sort(array, *count, sizeof(*array), fence_cmp, NULL);
+
+ /*
+ * Only keep the most recent fence for each context.
+ */
+ j = 0;
+ for (i = 1; i < *count; i++) {
+ if (array[i]->context == array[j]->context)
+ dma_fence_put(array[i]);
+ else
+ array[++j] = array[i];
+ }
+
+ *count = ++j;
+}
+
/* Implementation for the dma_fence_merge() marco, don't use directly */
struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
struct dma_fence **fences,
- struct dma_fence_unwrap *iter)
+ struct dma_fence_unwrap *iter,
+ enum dma_fence_unwrap_mode mode,
+ unsigned int *out_count)
{
struct dma_fence *tmp, *unsignaled = NULL, **array;
struct dma_fence_array *result;
ktime_t timestamp;
- int i, j, count;
+ int i, count;
+
+ if (mode == DMA_FENCE_UNWRAP_ARRAY) {
+ array = fences;
+ count = num_fences;
+
+ if (count > 1)
+ dma_fence_unwrap_dedup_sort(array, &count);
+
+ if (out_count)
+ *out_count = count;
+
+ return NULL;
+ }
count = 0;
timestamp = ns_to_ktime(0);
@@ -141,19 +177,7 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
if (count == 0 || count == 1)
goto return_fastpath;
- sort(array, count, sizeof(*array), fence_cmp, NULL);
-
- /*
- * Only keep the most recent fence for each context.
- */
- j = 0;
- for (i = 1; i < count; i++) {
- if (array[i]->context == array[j]->context)
- dma_fence_put(array[i]);
- else
- array[++j] = array[i];
- }
- count = ++j;
+ dma_fence_unwrap_dedup_sort(array, &count);
if (count > 1) {
result = dma_fence_array_create(count, array,
diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
index 66b1e56fbb81..b5683b024548 100644
--- a/include/linux/dma-fence-unwrap.h
+++ b/include/linux/dma-fence-unwrap.h
@@ -10,6 +10,18 @@
struct dma_fence;
+/**
+ * enum dma_fence_unwrap_mode - Mode of operation for fence unwrap and merge
+ * @DMA_FENCE_UNWRAP_MERGE: Merge all unsignaled fences into a new dma_fence object.
+ * Returns a single merged fence or stub.
+ * @DMA_FENCE_UNWRAP_ARRAY: Deduplicate and sort fences in-place.
+ * Returns nothing, but updates the input array and count.
+ */
+enum dma_fence_unwrap_mode {
+ DMA_FENCE_UNWRAP_MERGE, /* Return a single merged dma_fence or NULL on error */
+ DMA_FENCE_UNWRAP_ARRAY, /* Return deduplicated, sorted in-place array */
+};
+
/**
* struct dma_fence_unwrap - cursor into the container structure
*
@@ -50,7 +62,9 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
struct dma_fence **fences,
- struct dma_fence_unwrap *cursors);
+ struct dma_fence_unwrap *cursors,
+ enum dma_fence_unwrap_mode mode,
+ unsigned int *out_count);
/**
* dma_fence_unwrap_merge - unwrap and merge fences
@@ -58,6 +72,9 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
* All fences given as parameters are unwrapped and merged back together as flat
* dma_fence_array. Useful if multiple containers need to be merged together.
*
+ * Internally uses the DMA_FENCE_UNWRAP_MERGE mode to return a single merged
+ * dma_fence (or a stub if all fences are signaled).
+ *
* Implemented as a macro to allocate the necessary arrays on the stack and
* account the stack frame size to the caller.
*
@@ -69,7 +86,30 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
struct dma_fence *__f[] = { __VA_ARGS__ }; \
struct dma_fence_unwrap __c[ARRAY_SIZE(__f)]; \
\
- __dma_fence_unwrap_merge(ARRAY_SIZE(__f), __f, __c); \
+ __dma_fence_unwrap_merge(ARRAY_SIZE(__f), __f, __c, \
+ DMA_FENCE_UNWRAP_MERGE, NULL); \
+ })
+
+/**
+ * dma_fence_unwrap_shrink_array - Deduplicate and sort an array of fences in-place
+ * @ _num_fences: Number of input fences
+ * @ _fences: Array of dma_fence pointers to be deduplicated and sorted
+ * @ _out_fences: Output variable updated with the number of fences after deduplication
+ *
+ * This macro unwraps each fence (handling dma_fence_array if needed),
+ * filters out signaled fences, sorts the remaining ones by context and
+ * timestamp, and removes duplicates (keeping only the most recent fence per context).
+ *
+ * Internally uses the DMA_FENCE_UNWRAP_ARRAY mode to perform in-place filtering and
+ * sorting.
+ *
+ * The result is stored back in the input array (_fences) and the final count
+ * is written to @_out_fences. No memory allocation is performed.
+ */
+#define dma_fence_unwrap_shrink_array(_num_fences, _fences, _out_fences) \
+ ({ \
+ __dma_fence_unwrap_merge((_num_fences), (_fences), NULL, \
+ DMA_FENCE_UNWRAP_ARRAY, &_out_fences); \
})
#endif
--
2.34.1
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