Notes about NVMe Identify command

  • Opcode is 0x06.
  • The base address of the output (a single page) should be put in the DWORDs 6 and 7 of the command.
  • The low byte of command DWORD 10 indicates what is to be identified: 0 - a namespace, 1 - the controller, 2 - the namespace list.
  • If identifying a namespace, set DWORD 1 to the namespace ID.

virtio-net offloads reconfiguration

Virtio-net driver currently negotiates network offloads on startup via features mechanism and have no ability to disable and re-enable offloads later.
This patch introduced a new control command that allows to configure device network offloads state dynamically. The patch also introduces a new feature flag VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.

VIRTIO_NET_F_CTRL_GUEST_OFFLOADS (2) Control channel offloads reconfiguration support.

control virtqueue “Offloads State Configuration”.

Interrupt Coalescing under NVMe

Interrupt Coalescing

Interrupt coalescing, also known as interrupt moderation, is a technique in which events which would normally trigger a hardware interrupt are held back, either until a certain amount of work is pending, or a timeout timer triggers. Used correctly, this technique can reduce interrupt load by up to an order of magnitude, while only incurring relatively small latency penalties.