adstraw commented on code in PR #13844:
URL: https://github.com/apache/tvm/pull/13844#discussion_r1091231567
##########
src/runtime/hexagon/hexagon_buffer.cc:
##########
@@ -235,19 +245,20 @@ void hexagon_buffer_copy_across_regions(const BufferSet&
dest, const BufferSet&
// Finally, do the memory copies.
for (const auto& copy : macro_copies) {
- // clean Hexagon cache before / after memcpy to ensure clean cache state
to enable usage of DMA
- // bypass mode for increased DMA bandwidth
// TODO(HWE): Switch to ION Buffer to avoid need for memcpy and
potentially lighten or alleviate
// the burden of cache invalidation in this code
- qurt_mem_cache_clean(reinterpret_cast<qurt_addr_t>(copy.dest),
copy.num_bytes,
- QURT_MEM_CACHE_INVALIDATE, QURT_MEM_DCACHE);
- qurt_mem_cache_clean(reinterpret_cast<qurt_addr_t>(copy.src),
copy.num_bytes,
- QURT_MEM_CACHE_INVALIDATE, QURT_MEM_DCACHE);
memcpy(copy.dest, copy.src, copy.num_bytes);
+
+ // We must flush and invalidate both the destination and source of the
memcpy from the cache to
+ // ensure that DMA with cache bypass enabled will function properly. DMA
with cache bypass
+ // enabled assumes that HexagonBuffer objects are not cached unless
explicitly modified by the
+ // primfunc. We must flush and invalidate after the memcpy to uphold this
assumption. Note that
+ // we need not flush and invalidate prior to the memcpy because it is
coherent - issued through
+ // the cache.
qurt_mem_cache_clean(reinterpret_cast<qurt_addr_t>(copy.dest),
copy.num_bytes,
- QURT_MEM_CACHE_INVALIDATE, QURT_MEM_DCACHE);
+ QURT_MEM_CACHE_FLUSH_INVALIDATE, QURT_MEM_DCACHE);
qurt_mem_cache_clean(reinterpret_cast<qurt_addr_t>(copy.src),
copy.num_bytes,
- QURT_MEM_CACHE_INVALIDATE, QURT_MEM_DCACHE);
+ QURT_MEM_CACHE_FLUSH_INVALIDATE, QURT_MEM_DCACHE);
Review Comment:
Prefer to keep "flush and invalidate" on the destination which is safer (if
less performant) that a flush (only). The idea behind this PR, which is
captured in the comments, is that HexagonBuffer objects should not be in the
cache unless modified by the primfunc.
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