The pe2pe overview compared IPCQ (tl.send + tl.recv) against raw DMA
(tl.load + tl.store), but DMA is one-sided — DST never reads — while
tl.recv pays a slot-read on DST. The comparison was unfair: IPCQ
looked slower partly because it does more work.
Adds tl.recv_no_consume() — a separate, diagnostic-only entry point
that blocks for slot arrival but skips the slot-read (and bank-hop)
charge on DST. Production tl.recv is unchanged (no `consume` kwarg
on the public API), so the diagnostic flag can never accidentally
leak into real workloads.
Updates test_pe_to_pe_latency to call tl.recv_no_consume so the
overview.png shows IPCQ no-consume vs raw DMA on equal footing.
Also fixes PLOT_DIR back to docs/diagrams/pe2pe_latency_plots/
(was lost in a merge). Adds scripts/replot_pe2pe.py for label-only
re-renders without re-measuring.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Root cause: In ring all-reduce, PE_IPCQ's recv handler advances my_tail
and issues a credit return immediately. With tight credit latency
(0.12ns intra-cube), the sender can refill the slot BEFORE the
receiver's outbound PE_DMA reads from it for the next send. The
outbound snapshot then captures stale data from a later round.
Fix: Propagate TensorHandle.data (captured at recv-time, before credit
return) through the entire send chain:
tl.send(src=handle) → IpcqSendCmd.data → IpcqDmaToken.data
PE_DMA outbound already prefers token.data over MemoryStore read, so
the recv-time snapshot is used for the in-flight data. This eliminates
the race: the snapshot is captured before the slot can be overwritten.
Additional fixes:
- PE_MATH handle_command: compute SIMD latency from output tensor
element count via _compute_ns(), using max(overhead_ns, compute_ns).
Previously used overhead_ns=0.0 for all standalone MathCmd, making
math ops take 0ns in SimPy.
- DataExecutor secondary sort: same-t_start ops sorted by op_kind
(memory < gemm < math) so IPCQ slot writes execute before math reads.
- ipcq_copy recorded at INBOUND time (receiver PE_DMA arrival) instead
of outbound. Inbound time is after fabric propagation, so it sorts
correctly relative to the receiver's math.
- record_copy accepts explicit snapshot parameter (from token.data).
Result: N_ELEM=32 + 256-rank + n_slots=4 + cross-SIP now passes.
n_slots reverted to 4 (the deeper buffer was a workaround, not needed).
502 tests pass.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
tl.program_id(axis=0) returns local PE id within cube,
tl.program_id(axis=1) returns cube id. Enables cube-aware
sharding in benchmark kernels.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
mukesh
ywkang