SPDK will be able to fully saturate the PCIe bandwidth from a single CPU core here (no secret 6 threads inside the kernel). The drives are your bottleneck so it won't go faster, but it can use a lot less CPU.
But with SPDK you'll be talking to the disk, not to files. If you changed io_uring to read from the disk directly with O_DIRECT, you wouldn't have those extra 6 threads either. SPDK would still be considerably more CPU efficient but not 6x.
DDIO is a pure hardware feature. Software doesn't need to do anything to support it.
But with SPDK you'll be talking to the disk, not to files. If you changed io_uring to read from the disk directly with O_DIRECT, you wouldn't have those extra 6 threads either. SPDK would still be considerably more CPU efficient but not 6x.
DDIO is a pure hardware feature. Software doesn't need to do anything to support it.
Source: SPDK co-creator