The RSS hash threshold method looks like the only pseudo-random criterion that we can use that produces consistent result for every packet of a flow and does require more information. Of course elephant flows with an unlucky hash value might never get to use the EMC, but that risk we have with any stateless selection scheme.
[Darrell] It is probably something I know by another name, but JTBC, can you define the “RSS hash threshold method” ? I am referring to Billy's proposal (https://mail.openvswitch.org/pipermail/ovs-dev/2017-August/336509.html) In essence the is suggests to only select packets for EMC lookup whose RSS hash is above a certain threshold. The lookup probability is determined by the threshold (e.g. threshold of 0.75 * UINT32_MAX corresponds to 25%). It is pseudo-random as, assuming that the hash result is uniformly distributed, flows will profit from EMC lookup with the same probability. The new thing required will be the dynamic adjustment of lookup probability to the EMC fill level and/or hit ratio. [Darrell] Did you mean insertion probability rather than lookup probability ? No, I actually meant dynamic adaptation of lookup probability. We don't want to reduce the EMC lookup probability when the EMC is not yet overloaded, but only when the EMC hit rate degrades due to collisions. When we devise an algorithm to adapt lookup probability, we can study if it could make sense to also dynamically adjust the currently fixed (configurable) EMC insertion probability based on EMC fill level and/or hit rate. BR, Jan _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
