Messages in this thread | | | Date | Wed, 15 Sep 2010 12:10:00 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel |
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On Tue, Sep 14, 2010 at 11:21:15PM -0700, Shirley Ma wrote: > On Wed, 2010-09-15 at 07:12 +0200, Michael S. Tsirkin wrote: > > Yes, I agree this patch is useful for demo purposes: > > simple, and shows what kind of performance gains > > we can expect for TX. > > Any other issue you can see in this patch beside vhost descriptors > update?
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).
> 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 :)
-- MST
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