Re: [Xen-devel] xennet: skb rides the rocket: 20 slots

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-01-08 at 02:12 +0000, ANNIE LI wrote:

> >>
> >> I have added some extra info, but i don't have enough knowledge if
> >> this could/should be prevented from happening ?
> > MAX_SKB_FRAGS has never, AFAIK, been as big as 19 or 20 so I'm not sure
> > this can have ever worked.
> >
> > These SKBs seem to be pretty big (not quite 64KB), seemingly most of the
> > data is contained in a smallish number of frags, which suggests compound
> > pages and therefore a reasonably modern kernel?
> >
> > This probably relates somewhat to the issues described in the
> > "netchannel vs MAX_SKB_FRAGS" thread last year, or at least the solution
> > to that would necessarily involve fixing this issue.
> 
> If netback complains about "Too many frags", then it should be 
> MAX_SKB_FRAGS limitation in netback results in dropping packets in 
> netfront. It is possible that other netfronts(windows?) also hit this.

It's very possible. I rather suspect that non-Linux frontends have
workarounds (e.g. manual resegmenting etc) for this case.

Ian.


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