- KernelLaunchMsg gains target_start_ns: IO_CPU stamps a global barrier
(max path latency across every target PE), M_CPU passes it through,
PE_CPU yields until it before recording pe_exec_start. Every PE in a
launch begins kernel execution at the same env.now regardless of its
dispatch path length — eliminates per-PE dispatch-offset artifact in
cross-PE and cross-cube latency measurements.
- PE_DMA._handle_ipcq_inbound now pays Transaction.drain_ns at the top,
matching the terminal-drain behavior of ComponentBase._forward_txn for
every non-IPCQ Transaction. SRC-side tl.send stays fire-and-forget
(sender doesn't yield on sub_done); tl.recv now blocks until bytes
have actually drained into its inbox.
- ComponentContext: new compute_path_latency_ns helper + node_overhead_ns
field populated by GraphEngine.
- tests/test_kernel_launch_sync.py: asserts all PEs in one launch
produce identical pe_exec_ns for a no-op kernel (zero spread).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Adds tests/test_pe_to_pe_latency.py: a sweep that measures PE-to-PE
transfer latency for five hop types (intra-cube horizontal/vertical,
inter-cube horizontal/vertical, inter-SIP) across data sizes 128 B to
10 KB, on both the IPCQ (tl.send/tl.recv) and raw-DMA (tl.load+tl.store)
paths. Emits per-hop PNG plots, an overview PNG, and a CSV summary into
tests/pe2pe_latency_plots/. Latency is reported as max(pe_exec_ns) across
participating PEs, read from engine.get_completion(), so the measurement
captures the SRC/DST PE's kernel body time rather than the full launch+
response-aggregation envelope.
Two simulator fixes were needed to make this measurement meaningful:
- PeMMU now stores a list of (start, end, pa) sub-regions per page
rather than a single PA. DPPolicy layouts with shards smaller than
page_size (e.g. 128 B payloads with 4 KB pages) used to silently
overwrite each other through last-write-wins, causing DMAs intended
for cube0 to physically route to cube3 - inflating latency by ~170 ns
per DMA at small sizes. STOPGAP: real MMUs don't support sub-page
regions; long-term fix is either smaller MMU page size or DPPolicy
validation that refuses sub-page shards.
- M_CPU's per-PE metrics aggregation (pe_exec_ns, dma_ns, compute_ns)
now max-merges against the existing value in result_data rather than
overwriting. Multi-cube workloads share one result_data dict via
IO_CPU fanout; the previous overwrite caused whichever cube's M_CPU
finished last to clobber others' values, so multi-cube pe_exec_ns was
racy and frequently 0. Same fix applied in legacy/builtin/m_cpu.py.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
mukesh
ywkang