On 26 May 2017 at 07:00, Zoltán Balogh <[email protected]> wrote: > > Hi Joe, > >> Backing up a bit for context, the stats attribution goes roughly like this: >> * First upcall, handler thread calls through the translate code with a >> packet. The resubmit_stats are derived from that packet. This goes >> through xlate_actions(). >> * First dump of flow from revalidator thread fetches the flow and runs >> the same xlate_actions() with whatever stats it has (may be zero). >> This time, whenever stats attribution or side effects occur, an >> xlate_cache entry is generated. >> * Second and subsequent dumps of flows fetches the flow and shortcuts >> the xlate_actions() by using the xlate_cache instead - ie a call to >> xlate_push_stats(). >> >> So, in the same place where the resubmit_stats is manipulated, you >> would also need to generate a new XC entry which would manipulate the >> stats - this would be a 'side-effect'. I'd imagine that prior to the >> full output translation there would be a XC_TRUNCATE(truncated_size) >> then afterwards there would be an XC_TRUNCATE_RESET(). Or it could be >> just XC_SET_SIZE(...) where 0 is reset and non-zero is a truncate >> size. In the implementation/execution in xlate_push_stats() when >> performing XC_TRUNCATE you would need to store the original push_stats >> size somewhere, then calculate a new 'n_bytes' based on the number of >> packets and existing bytes*. For XC_TRUNCATE_RESET(), it would restore >> the original push_stats size. > > Thank you for the explanation. > >> * Hmm, I'm not sure the calculation will be 100% here. Let's say there >> were 3 packets hit the flow, 50B, 200B, 300B. If output(max_len=100) >> was executed, then we don't know how many of the packets were >> truncated. The maximum number of bytes that could be transmitted is >> 300, but the actual number was 250. We could divide the n_bytes by >> n_packets, subtract the max_len and then multiply back up by the >> number of packets, which works for this case assuming floating point >> arithmetic but is slightly off if using integer math.. > > I don't think, that would be the proper way of calculating n_bytes. Let's > say we have 3 packets with 50B, 200B, 200B and max_len=100. The output > should be 50 + 100 + 100 = 250B. > Following the instructions above we will get > [(50 + 200 + 200) / 3 - 100 ] * 3 = [450 / 3 - 100 ] * 3 = 50 * 3 = 150B > > Any other idea how to calculate the truncated size with xlate cache? > Or maybe I did not understand your calculation.
Nope, you're absolutely right. It occurred to me a little later that for more complex statistic sets this doesn't work. I suspect you actually need datapath support for tracking these stats separately. > There is one more thing to be taken into consideration. By adding a tunnel > header, the size of packets increases as well. But that's a constant value > for each packet, easier to calculate with it. Good point. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
