On Fri, Jun 10, 2016 at 12:11:58PM -0700, Ritun Patney wrote: > I am studying the network performance between a pair of KVM workloads > on different hosts. I have been looking into the RX, TX data path when > a vhost-net driver is involved. > > I am intrigued why does a packet transmission from a guest run > entirely in the context of the vhost thread. From what I could gather > from the source, the vhost driver seems to write packets to the tap > device using sendmsg. The tap device seems to enqueue it for napi to > take over. I would have assumed that after sending the packet over the > tap device, a softirq would have taken over but that doesn't happen. > > I am wondering how it that the entire packet is processed in the vhost > kernel thread's context and would appreciate help! The way I read the drivers/net/tun.c code the local softirq processing happens immediately in netif_rx_ni(). So progress should be made immediately during ->sendmsg() rather than just marking the softirq pending and returning back to vhost_net.ko. Stefan
Attachment:
signature.asc
Description: PGP signature
