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If we move setup_ddp() earlier as you suggested, it can >> result it running on the wrong CPU. > > Please define wrong CPU. Let's say we connect with 1 IO queue on CPU 0. We run our application which run IOs on multiple CPU cores (0 and 7 as an example). Whenever the IO was issued on CPU 7, setup_cmd_pdu() and queue_request() will be run in the context of CPU 7. We consider CPU 7 "wrong", because it isn't q->io_cpu (CPU 0). It's only after queue_request() dispatches it that it will it run on CPU 0. > But the sk_incmoing_cpu is updated with the cpu that is reading the > socket, so in fact it should converge to the io_cpu - shouldn't it? Yes, that is true. > Can you please provide a concrete explanation to the performance > degradation? We believe the setup_ddp should be called from the CPU core on which the nvme queue was created so all the IO path SW-HW interaction will run on the same CPU core. The performance degradation is relevant only to specific cases in which the application will run on the "wrong" CPU core on which the NVMe queue was not created. If you don=E2=80=99t see it as a problem, we can move the setup_ddp to setup_cmd_pdu(). Thanks