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    SubjectRe: [PATCH net-next RFC 0/5] xen-netback: TX grant mapping instead of copy
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    On Thu, 2013-12-12 at 22:08 +0000, Zoltan Kiss wrote:
    > On 28/11/13 17:43, Ian Campbell wrote:
    > > On Thu, 2013-11-28 at 17:37 +0000, Zoltan Kiss wrote:
    > > Routing/firewalling domUs is as valid as bridging. There is nothing in
    > > the slightest bit suboptimal about it.
    > >
    > > If this use case regresses with this approach then I'm afraid that
    > > either needs to be addressed or a different approach considered.
    > >
    > >> Anyway, I will try this out, and see if it really copies everything, and
    > >> get some numbers as well.
    > >
    > > Thanks.
    >
    > Now I managed to try it out. As I expected, Dom0 does copy the mapped
    > page. The peak throuhput I could get was 6.6 Gbps, however it could keep
    > that only for short periods, I guess when the unmapping was ideally
    > batched. The average was 5.53.
    > On the same machine the same 10 min iperf session, without my patches
    > made the peak 5.9 while the average was 5.65. Do you think it is an
    > acceptable regression?

    Well, it would of course be preferable to avoid it. I'm quite reluctant
    to see this scenario become a second class citizen.

    > I used 3.12 Dom0 and guest kernel, the guest transmitted though a 10Gb
    > card to a bare metal box.
    > I plan to look further if we can avoid somehow this:
    >
    > https://lkml.org/lkml/2012/7/20/363
    >
    > So then this scenario can benefit from grant mapping.
    >
    > Regards,
    >
    > Zoli




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