lkml.org 
[lkml]   [2013]   [Nov]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH net-next RFC 0/5] xen-netback: TX grant mapping instead of copy
    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


    \
     
     \ /
      Last update: 2013-11-28 18:41    [W:2.846 / U:0.372 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site