Messages in this thread | | | Date | Thu, 28 Nov 2013 17:37:32 +0000 | From | Zoltan Kiss <> | Subject | Re: [PATCH net-next RFC 0/5] xen-netback: TX grant mapping instead of copy |
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On 07/11/13 10:52, Ian Campbell wrote: > On Fri, 2013-11-01 at 19:00 +0000, Zoltan Kiss wrote: >> On 01/11/13 10:50, Ian Campbell wrote: >>> Does this always avoid copying when bridging/openvswitching/forwarding >>> (e.g. masquerading etc)? For both domU->domU and domU->physical NIC? >> I've tested the domU->domU, domU->physical with bridge and openvswitch >> usecase, and now I've created a new stat counter to see how often copy >> happens (the callback's second parameter tells you whether the skb was >> freed or copied). It doesn't do copy in all of these scenarios. >> What do you mean by forwarding? The scenario when you use bridge and >> iptables mangling with the packet, not just filtering? > > I mean using L3 routing rather L2 bridging. Which might involve > NAT/MASQUERADE or might just be normal IP routing. I still couldn't find time to try out this scenario, but I think in this case packet goes through deliver_skb, which means it will get copied. So performance would be a bit worse due to the extra map/unmap. And I'm afraid we can't help that too much due to this: https://lkml.org/lkml/2012/7/20/363 However I think using Dom0 as a router/firewall is already a suboptimal solution, so maybe a small performance regression is acceptable? Anyway, I will try this out, and see if it really copies everything, and get some numbers as well.
>>> How does it deal with broadcast traffic? Now I had time to check it: broadcast packets get copied only once, when cloning happens. It will swap out the frags with local ones, so any subsequent cloning will have a local SKB.
Zoli
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