The Bottleneck Was the PCIe Link, Not the Code
GPU idle was 60 percent of decode wall time, and the largest share was host-to-device copies running at 3.1 to 3.4 GB/s against 28.5 GB/s on a healthy boot. The root port negotiated 2.5 GT/s. Several timed A/Bs from that boot are void, one fusion ratio survives, and the machine is still on the slow link.
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