On Mon, 2014-01-20 at 21:24 +0000, Zoltan Kiss wrote: > A long known problem of the upstream netback implementation that on the TX > path (from guest to Dom0) it copies the whole packet from guest memory into > Dom0. That simply became a bottleneck with 10Gb NICs, and generally it's a > huge perfomance penalty. The classic kernel version of netback used grant > mapping, and to get notified when the page can be unmapped, it used page > destructors. Unfortunately that destructor is not an upstreamable solution. > Ian Campbell's skb fragment destructor patch series [1] tried to solve this > problem, however it seems to be very invasive on the network stack's code, > and therefore haven't progressed very well. > This patch series use SKBTX_DEV_ZEROCOPY flags to tell the stack it needs to > know when the skb is freed up. That is the way KVM solved the same problem, > and based on my initial tests it can do the same for us. Avoiding the extra > copy boosted up TX throughput from 6.8 Gbps to 7.9 (I used a slower > Interlagos box, both Dom0 and guest on upstream kernel, on the same NUMA node, > running iperf 2.0.5, and the remote end was a bare metal box on the same 10Gb > switch) > Based on my investigations the packet get only copied if it is delivered to > Dom0 stack,
This is not quite complete/accurate since you previously told me that it is copied in the NAT/routed rather than bridged network topologies. Please can you cover that aspect here too. Ian. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
