vsock: Have two separate threads for handling TX and RX

[techiepriyansh]

Currently, the VhostUserVsockBackend handles both TX and RX in a single thread. It would be nice to have two separate threads handling TX and RX.

Implementing this would involve the following:

• Define two threads in VhostUserVsockBackend with the appropriate queue_masks: 1 for the RX thread and 2 for the TX thread.
• Set the TX thread's vring worker to also listen for BACKEND_EVENTs by calling set_vring_worker during initialization in start_backend_server.
• Handle RX or TX in VhostUserVsockBackend::handle_event depending on the thread_id.
• Refactor the hashmaps and backend_rxq contained in VsockThreadBackend to be accessible by both the threads (maybe over an RwLock).
• Make the option to choose between single-threaded or multi-threaded configurable by the user.

[stefano-garzarella]

Thank you for the analysis! If you have time and interest to start this work, go ahead, otherwise we'll do it later because it would be a great cleanup.

[techiepriyansh]

Yes, I'll get to it in a few days.

[ramyak-mehra]

Hey i see this hasn't been picked up in quite some time. If no one is picking this up shall i do it?

[stefano-garzarella]

@ramyak-mehra great! yes please, go head.

IIUC @techiepriyansh is busy, but feel free to ping us if the situation is changed.