[ovs-discuss] What does “require user space processing” mean for missed packets in ovs-dpctl show output?

Justin Pettit jpettit at ovn.org
Thu May 2 22:37:08 UTC 2019


> On May 2, 2019, at 1:05 PM, Daniel H <grokit at gmx.ch> wrote:
> 
> In the manual of ovs-dpctl it says:
>  
> [...]
> "missed" displays the number of packets not matching any existing flow and require user space processing.
> "lost" displays number of packets destined for user space process but subsequently dropped before reaching userspace.
> [...]
> 
> Questions:
> What exactly is meant by "require user space processing"?
> As I see a lot of packets (43777102357, looks like every 3rd packet) with the tag "missed", I'd like to understand what happens with those packets exactly?

It means that the kernel module needs to be told what to do with the packet by ovs-vswitchd.  Most of the complicated processing logic is in ovs-vswitchd, and the datapath is essentially a cache of recently seen traffic.  That "missed" count is usually for new flows for which there's no entry in the datapath yet.  However, there are cases that require userspace processing (e.g., L2 learning).

I agree that that ratio isn't very good.  It looks like that machine is running a version of OVS that could be over five years old.  What version of OVS is it running?  Is it using a version that includes megaflows?  Is ovs-vswitch and the OVS kernel module the same version?

--Justin




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