feat(comm): add copy-engine selected-record exchange with bulk layer packets

README.md

@@ -120,6 +120,23 @@ Set `SPARKINFER_PRINT_COMPILE_PROGRESS=1` to log each compiler invocation with i
 cache-key parameters and duration — useful for figuring out what warmup
 actually covered. `SPARKINFER_TIMING=1` enables per-kernel timing logs.
 
+### Selected-record copy exchange
+
+`sparkinfer.comm.pcie.SelectedRecordCopyExchange` moves sparse, fixed-width
+records between CUDA-IPC peers through the PCIe copy engine. `exchange()`
+handles one record plane. `exchange_layers()` packs three planes with one
+destination map, issues one rotated DMA exchange and arrival barrier, then
+unpacks the planes into caller-owned outputs. The layered layout overlays the
+same IPC slab; `layered_max_records` reports its bounded capacity so callers can
+fall back to `exchange()` when needed.
+
+All ranks must call exchanges in the same order and with rank-consistent active
+record counts. One exchange object is stream-affine. Run one eager exchange on
+that stream before CUDA graph capture, then replay it on the same stream. The
+balanced deferred-release protocol makes single-layer, three-layer, and empty
+exchanges safe to alternate, but `close()` must run before the process group is
+destroyed.
+
 ## Where to look next
 
 - `tests/` is the executable spec — per-group API and numerical-reference

sparkinfer/comm/pcie/__init__.py

@@ -13,6 +13,8 @@
 - ``DcpAllToAll``: DCP attention exchange with fused LSE reduce-scatter.
 - ``SelectedRecordExchange``: direct peer writes for destination-selected,
   fixed-width records.
+- ``SelectedRecordCopyExchange``: compact, copy-engine transfer, and unpack
+  for destination-selected fixed-width records.
 
 Raw CUDA (not CuTe): each class JIT-builds its colocated ``.cu`` via
 torch.utils.cpp_extension, so nvcc must be available at runtime.
@@ -37,6 +39,7 @@
         "DcpAllToAllPool",
         "SelectedRecordExchange",
         "SelectedRecordExchangeInitializationError",
+        "SelectedRecordCopyExchange",
         "autotune_dma_crossovers",
         "parse_oneshot_max_size",
         "lse_reduce_scatter_reference",
@@ -63,6 +66,7 @@
         OneshotAllReducePool,
         SelectedRecordExchange,
         SelectedRecordExchangeInitializationError,
+        SelectedRecordCopyExchange,
         TwoShotReduceScatter,
         autotune_dma_crossovers,
         is_supported,

sparkinfer/comm/pcie/api.py

@@ -33,6 +33,9 @@
 from .pcie_selected_records import (
     PCIeSelectedRecordExchangeInitializationError as SelectedRecordExchangeInitializationError,
 )
+from .pcie_selected_records_ce import (
+    PCIeSelectedRecordCopyExchange as SelectedRecordCopyExchange,
+)
 from .pcie_twoshot import (
     PCIeTwoShotSP as TwoShotReduceScatter,
 )
@@ -58,6 +61,7 @@ def is_supported(device=None) -> bool:
     "DcpAllToAllPool",
     "SelectedRecordExchange",
     "SelectedRecordExchangeInitializationError",
+    "SelectedRecordCopyExchange",
     "autotune_dma_crossovers",
     "parse_oneshot_max_size",
     "lse_reduce_scatter_reference",