I want the sFlow module to know when a sampled packet was a cache miss in the datapath. That way we can include this information with the sFlow sample feed that is sent out, and applications can analyze the data to see what mix of traffic is suffering cache misses. Any ideas on how to add this?
When a cache miss is upcall'd to userspace (from In datapath/datapath.c:ovs_dp_process_packet()), then userspace reacts by pushing down operations to create a new flow and send that packet (lib/dpif-netlink.c:dpif_operate()). But if that packet is then sampled and upcall'd to sFlow there does not seem to be a flag we can inspect to know that it was a cache miss in the first place. If the datapath were to include the number of packets seen by the flow so far when it upcalls a sample (that number is kept in struct sw_flow in the datapath flow cache) then we could infer it was a cache miss when we see that number == 1. Alternatively, if we could set a bit somewhere when we pass the cache-miss back down to be sent, so that the bit is preserved and visible if that same packet is then sampled, then we could do it that way. Trying to avoid datapath changes I looked to see if there was a way to set a bit in the skbuff that would survive and come back in a sample, but I'm not sure how to go about doing that. Or maybe there is another way? Neil ------ Neil McKee InMon Corp. http://www.inmon.com _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
