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    SubjectRe: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel
    On Wed, Sep 15, 2010 at 05:04:12PM +0200, Michael S. Tsirkin wrote:
    > On Wed, Sep 15, 2010 at 07:52:34AM -0700, Shirley Ma wrote:
    > > On Wed, 2010-09-15 at 12:10 +0200, Michael S. Tsirkin wrote:
    > > > Another issue is that macvtap can be bound to almost
    > > > anything, including e.g. a tap device or a bridge,
    > > > which might hang on to skb fragments for unlimited time.
    > > > Zero copy TX won't easily work there.
    > > > I can imagine either somehow triggering a data copy after the
    > > > fact (hard), or detecting such devices and avoiding
    > > > zero copy (unfortunate for guest to guest, and drivers
    > > > will need tuning).
    > >
    > > So far macvtap zero copy patch is limited to lower devices supports high
    > > memory DMA, it doesn't apply to a tap device or a bridge.
    >
    > Okay. What about macvtap in bridge mode?

    In fact, I rechecked: both bridge and loopback have NETIF_F_HIGHDMA set.
    So maybe we should check NETIF_F_NETNS_LOCAL ...

    macvtap in bridged mode is interesting as well.

    > > > > Don't you think once I address vhost_add_used_and_signal update
    > > > > issue, it is a simple and complete patch for macvtap TX zero copy?
    > > > >
    > > > > Thanks
    > > > > Shirley
    > > >
    > > > I like the fact that the patch is simple. Unfortunately
    > > > I suspect it'll stop being simple by the time it's complete :)
    > >
    > > I can make a try. :)
    > >
    > > Thanks
    > > Shirley


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