[ovs-discuss] Drops in OVS

Abhishek Verma abhishekv.verma at gmail.com
Sun Aug 2 02:19:56 UTC 2015


Is my understanding below correct?

On Fri, Jul 31, 2015 at 10:14 AM, Abhishek Verma <abhishekv.verma at gmail.com>

> Hi Flavio,
>> > Is this correct?
>> No, there is a cache in the kernel which is periodically refreshed or
>> empty at the initialization.  When the first packet comes in the
>> packet is queued to the userspace daemon which will update the
>> kernel's cache.  Next packets matching the cached flow will pass
>> directly.
> Aha. So, the of-ctl add-flow really adds a flow only in the User Space and
> nothing in the kernel space. If this flow rule isnt added then all packets
> will hit the default rule where we do normal L2 learning and switching. By
> adding of-ctl add-flow rules we simply over-ride that behavior.
> The real flows that get added by the user space daemon that the packets
> actually hit can be viewed by "ovs-dpctl dump-flows".
> Is this how it is?
>> However, depending on how you programmed your flows and the traffic,
>> you could see a burst coming for a flow that isn't cached yet. Since
>> the queue is limited, it can overflow.
> Ok, and these drops are visible when i give "ovs-dpctl show" command. Is
> there a way to increase this queue size?
> Flows afaik are always timed out after 5 secs. Assume i have an
> application that bursts every 6 secs. In that case i always run the risk of
> losing packets. Is there a way to pin a flow or increase its timeout value?
> Thanks, Abhishek
Thanks, Abhishek
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