[ovs-discuss] Packet drops with high rate of Packet_In

Ben Pfaff blp at nicira.com
Mon Nov 25 18:08:37 UTC 2013


On Mon, Nov 25, 2013 at 03:15:07PM +0100, Anton Matsiuk wrote:
> as Open vSwitch stores only 256 Packet_Ins in buffer (OFPT_FEATURES_REPLY:
> n_buffers = 256) after 256 packets it sets Buffer_ID to 0xffffffff.
> Controller didn't check this value as incorrect and placed it into
> responses in flow_mods and packet_outs, that caused packet drops after
> approximately 300 packet_in in a burst.
> 
> BTW, setting miss_send_len = 65535 forces switch to send complete Packet_In
> to Controller but switch still stores packets in buffer and adds valid
> buffer_id for first 255 of them. Is it possible to turn off buffering in
> switch (and to set buffer_id = -1 for all packets) using OpenFlow 1.0? (In
> OpenFlow 1.2+ it should be possible by setting OFPCML_NO_BUFFER as I
> understood).

I think that we recently changed OVS to not buffer any packets sent
with a miss_send_len of 65535.  Have you tried with OVS 2.0 or later?

> Is it possible to vary the size of buffer for Packet_In in Open vSwitch?

No, this is the first request I've heard for that feature.  (I've
often thought about just removing packet buffering entirely, it's
always been optional in OpenFlow and I'm not convinced it is useful.)



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