On Tue, Mar 30, 2021 at 11:16:48PM +0200, Ilya Maximets wrote: > On 3/3/21 3:46 PM, [email protected] wrote: > > From: Tonghao Zhang <[email protected]> > > > > If user don't set the meter "burst_size", when creating them. OvS > > will set "brust_size" to "rate", and there will be a double "rate" > > as burst rate. For example: > > > > $ ovs-ofctl -O OpenFlow13 add-meter br0 'meter=1 pktps stats > > bands=type=drop rate=1000000' > > > > The rate expected is 1Gbps, but burst rate is 2Gbps while > > we don't use "burst_size". > > > OpenFlow spec is a bit loose in definition of what should > be behavior if burst is not set: > """ > If the flag OFPMF_BURST is not set the burst_size values from meter > bands are ignored, and if the meter implementation uses a burst value, > this burst value must be set to an implementation defined optimal value. > """ > > In our case, historically, "implementation defined optimal value" was > value equal to rate. I have no idea why, but it's hard to argue with > it since the spec gives a great freedom to choose. > > Actually, the "burst" itself as a term makes very little sense to me. > It's defined by the spec as: > """ > It defines the granularity of the meter band, for all packet or byte > bursts whose length is greater than burst value, the meter rate will > always be strictly enforced. > """ > > But what is the burst? How the implementation should define which > packets are in the burst and which are from the next one? > > Current implementation just assumes that bursts are measured per second. > But the rate is measured per second too. So, burst and rate is > essentially the same thing and implementations just sums them together > to get the bucket size. So, I do not understand why "burst" and > "burst_size" exist at all. Why not just set the rate a bit higher? > > Ben, can you shed some light on this? What was the original idea > behind the meter burst? Or maybe I'm missing something?
I wasn't really involved in the design of meters. I saw them as a feature of hardware switches that was not very relevant to software switches. I guess I was wrong. I think that Jean Tourillhes was the primary architect of meters in OpenFlow. I am adding him to this thread. I hope that he can help. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
