Messages in this thread | | | Date | Mon, 24 Feb 2014 15:31:17 +0000 | From | Zoltan Kiss <> | Subject | Re: [PATCH net-next v5 0/9] xen-netback: TX grant mapping with SKBTX_DEV_ZEROCOPY instead of copy |
| |
On 19/02/14 09:50, Ian Campbell wrote: > 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. Ok.
Zoli
| |