Hi Ben, Thanks for your detailed reply. Does this mean that every time a packet arrives, it is first sent to the user process vswitchd and then sent back into the kernel for forwarding, which means there will be a kernel-to-user space and back to kernel space context switch for every packet that arrives? In that case, how is the performance better than that of say vde switch?
Thanks, Aish On Tue, Sep 20, 2011 at 9:31 PM, Ben Pfaff <[email protected]> wrote: > On Tue, Sep 20, 2011 at 09:18:46PM -0700, Aishwarya wrote: > > The instructions to start openvswitch say we need to run ovsdbserver > > (listening on a unix socket in my case), and vswitchd subsequently. Now, > > openvswitch is said to route packets in the kernel itself and not use > > userspace. > > The Open vSwitch kernel module does almost nothing on its own > initiative. Userspace and in particular ovs-vswitchd is a vital part of > setting up flows. > > > However, ovsdb-server and vswitchd are user processes. What is the > > role of these actually when 2 vms are trying to send traffic via the > > openvswitch? > > When a new flow arrives, ovs-vswitchd decides where its packets should > go. > > > Lets say I configure the flow rules and then kill the vswitchd > > process, the vms cannot communicate anymore. Why should this happen > > although the kernel module is still loaded? How is the routing of the > > packet being affected by these user level processes? > > When new flow arrives, ovs-vswitchd isn't running so it can't decide > where the packets should go. They get dropped. > > > I would assume that the database server would be needed only to query > > something like port or flow information. But it seems to be necessary > > while sending traffic too. Is this because the switch on receiving > > traffic is querying the database to check for the flows, before > > sending the traffic out? > > No. > > > In that case, what does it mean that openvswitch has High-performance > > forwarding using a Linux kernel module (since it is using the user > > space program as well?) > > Once ovs-vswitchd decides where packets in a flow should go, they get > forwarded quickly by the kernel. >
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