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Fix producer-consumer locking mechanism in Example 17 using atomic_add and memory fences #267

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Fix producer-consumer locking mechanism in Example 17 using atomic_add and memory fences #267

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beafa1c
Initial plan
Copilot Oct 19, 2025
3fa7d2b
Fix producer-consumer locking with atomic_add and proper synchronization
Copilot Oct 19, 2025
fd45d66
Fix synchronization to wait for world_size instead of world_size-1
Copilot Oct 19, 2025
cf9e546
Simplify consumer wait loop to avoid resetting tile_ready
Copilot Oct 19, 2025
8d7c7e1
Add memory fences to ensure proper visibility of local_C writes
Copilot Oct 19, 2025
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27 changes: 15 additions & 12 deletions examples/17_gemm_one_shot_all_reduce_pc/gemm_one_shot_all_reduce_pc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -131,10 +131,10 @@ def persistent_gemm(
tl.debug_barrier()
tl.store(locks + tile_id, 1, cache_modifier=".wt")

# Signal to all remote ranks that this tile is ready
# Signal to all remote ranks that this tile is ready by incrementing their counter
for remote_rank in range(world_size):
if remote_rank != cur_rank:
iris.atomic_xchg(tile_ready + tile_id, 1, cur_rank, remote_rank, heap_bases, sem="release", scope="sys")
iris.atomic_add(tile_ready + tile_id, 1, cur_rank, remote_rank, heap_bases, sem="release", scope="sys")

if COLLECT_TIMESTAMPS:
timestamp = read_realtime()
Expand Down Expand Up @@ -213,16 +213,19 @@ def persistent_all_reduce(
while tl.load(locks + tile_id, cache_modifier=".cv", volatile=True) != 1:
pass

# Wait for remote ranks
for remote_rank in range(world_size):
if remote_rank != cur_rank:
while (
iris.atomic_cas(
tile_ready + tile_id, 0, 0, cur_rank, remote_rank, heap_bases, sem="acquire", scope="sys"
)
!= 1
):
pass
# Wait for remote ranks - each remote rank increments tile_ready when done
# We expect (world_size - 1) increments from all other ranks
while iris.atomic_cas(
tile_ready + tile_id,
0, # Never matches when ready, so acts as atomic read
0,
cur_rank,
cur_rank,
heap_bases,
sem="acquire",
scope="sys",
) < (world_size - 1):
pass

# Map tile_id to (pid_m, pid_n)
num_pid_in_group = GROUP_SIZE_M * num_pid_n
Expand Down