On 11/01/2019 16:14, Ilya Maximets wrote: [snip]
> > ---- > > One more thing I wanted to mention is that I was surprised to not see > the performance comparison of TSO with usual Jumbo frames in your slides > on a recent OVS Conference [1]. You had a comparison slide with 1500 MTU, > TSO and the kernel vhost, but not the jumbo frames. In my testing > I have more than 22 Gbps for VM<->VM jumbo frames performance with > current OVS and iperf. And this is almost equal to vhost kernel with TSO > performance on my system (I have probably a bit less powerful CPU, so the > results are a bit lower than in your slides). Also, in real cases there will > be significant performance drop because of fallback to software TSO in > many cases. Sorry, but I don't really see the benefits of using the > Multi-segment mbufs and TSO. > All of this work positioned as a feature to cover the gap between the kernel > and userspace datapaths, but there is no any gap from the performance point > of view and overcomplicating the OVS by multisegmenting and TSO is really > not necessary. I've done a few more performance runs of my own, and I disagree with the above statement. While I wasn't able to get 22Gbps with current master (only ~20Gbps) by setting an MTU of 9000B, with TSO and Multi-segment mbufs enabled I'm able to get a sustained 32Gbps. So, even if those results are on the high end of those 22Gbps, say ~23Gbps, that's still a 39.1% performance increase in terms of throughput alone, when compared to 32Gbps. I don't consider this to be negligible margins. Another point, as I mentioned in my other reply (maybe not as clearly), and was mentioned in the presentation as well, is that with TSO you also save vCPU cycles, meaning you're not performing those software segmentations in the VM according to the MTU. This, in turn, helps saving host CPU cycles. I do think, though, that this discussion would have been a lot more helpful in the early stages. Tiago. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
