[ovs-dev] [PATCH] dpif-netdev: Refactor datapath flow cache

[Wang, Yipeng1]

>-----Original Message-----
>> I think this is an interesting idea.
>>
>> One caveat is that in this case we use the rules' field to infer the flows' field. If the rule
>> does not consider a field within which the flow has high entropy, it still does not help.
>> Or if the rule considers many fields but the flow does not have high entropy there, then
>> we add the incremental software hash overhead for little benefit.
>>
>> I am not sure if that is common in real cases, I am more concerned with the second scenario,
>> what do you think?
>>
>Yes, you're right.
>I don't have any good solution, but are we able to observe from the
>subtable entries or its statistics to see whether a field has high
>entropy? So in your second scenario, we don't have to add all new
>fields into the hash but only a subset of them.
>

[Wang, Yipeng] 
To profile entropy I believe sampling the packets into a bloomfilter/bitmap could do the job.
But I think eventually people will debate on If the profiling cost and code complexity worth the effort or not.

>> We should profile a little bit to see how much overhead the incremental CRC will
>> cost.
>>
>That would be very helpful!
>Thanks
>William