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GPU Metal: fence only threadgroup memory in the work-group collectives - #16126
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The Metal work-group scan, reduction and broadcast exchange data through threadgroup memory only, so their barriers need not order device memory. GPUbarrier() fences both, which on Apple GPUs makes each barrier wait for the outstanding device-memory accesses. With threadgroup-only fences the stream-compaction scanStart takes 12% less GPU time (30 kHz Pb-Pb, 1/4 TF, no --debug, 3 interleaved rounds); results unchanged.
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Metal only. |
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The Metal work-group scan, reduction and broadcast exchange data through
threadgroup memory only, so their barriers need not order device memory.
GPUbarrier() fences both, which on Apple GPUs makes each barrier wait for
the outstanding device-memory accesses. With threadgroup-only fences the
stream-compaction scanStart takes 12% less GPU time (30 kHz Pb-Pb, 1/4 TF,
no --debug, 3 interleaved rounds); results unchanged.