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RE: [PATCH] net: add per device sg_max_frags for skb

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From: Hans Westgaard
> Sent: 08 January 2016 09:56
...
> >> The patch allows the device to limit the maximum number fragments used
> >> in one skb.
> >
> > This doesn't seem to me to be the correct way to fix this.
> > Anything that adds an extra fragment (in this case IPoIB) should allow
> > for the skb already having the maximum number of fragments.
> > Fully linearising the skb is overkill, but I think the first fragment
> > can be added to the linear part of the skb.
> >
> > 	David
> >
> >
> When IpoIB handles a skb-request it converts fragments to SGEs to
> be handled by a HCA.
> The problem arises when the HCA have a limited number of SGEs less than
> MAX_SKB_FRAGS.
> (it gets a little worse since IPoIB need to yet another segment)
> I have not found any easy way of fixing this with currenct codebase.

I think one of the xen ethernet interfaces had a similar problem.

Just reduce the number of fragments by copying two (or more) of them
into a single fragment.
In effect, anything that reduces the number of fragments will do a copy.

	David

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[PATCH] net: add per device sg_max_frags for skb Hans Westgaard Ry <hans.westgaard.ry@oracle.com> - 2016-01-06 14:20 +0100
  RE: [PATCH] net: add per device sg_max_frags for skb David Laight <David.Laight@ACULAB.COM> - 2016-01-06 15:10 +0100
    Re: [PATCH] net: add per device sg_max_frags for skb Hans Westgaard Ry <hans.westgaard.ry@oracle.com> - 2016-01-08 11:00 +0100
      RE: [PATCH] net: add per device sg_max_frags for skb David Laight <David.Laight@ACULAB.COM> - 2016-01-08 11:40 +0100
      Re: [PATCH] net: add per device sg_max_frags for skb Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-01-08 12:50 +0100
        Re: [PATCH] net: add per device sg_max_frags for skb Hans Westgaard Ry <hans.westgaard.ry@oracle.com> - 2016-01-13 15:00 +0100
          Re: [PATCH] net: add per device sg_max_frags for skb Eric Dumazet <edumazet@google.com> - 2016-01-13 15:30 +0100
          Re: [PATCH] net: add per device sg_max_frags for skb Eric Dumazet <edumazet@google.com> - 2016-01-13 15:30 +0100
            Re: [PATCH] net: add per device sg_max_frags for skb Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-01-13 16:10 +0100
            Re: [PATCH] net: add per device sg_max_frags for skb David Miller <davem@davemloft.net> - 2016-01-13 16:40 +0100
              Re: [PATCH] net: add per device sg_max_frags for skb Eric Dumazet <edumazet@google.com> - 2016-01-13 16:50 +0100
          Re: [PATCH] net: add per device sg_max_frags for skb ebiederm@xmission.com (Eric W. Biederman) - 2016-01-13 22:20 +0100
  Re: [PATCH] net: add per device sg_max_frags for skb Eric Dumazet <eric.dumazet@gmail.com> - 2016-01-06 15:10 +0100
    Re: [PATCH] net: add per device sg_max_frags for skb Hans Westgaard Ry <hans.westgaard.ry@oracle.com> - 2016-01-08 11:10 +0100

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