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From: David Laight <David.Laight@ACULAB.COM>
To: "'Herbert Xu'" <herbert@gondor.apana.org.au>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>
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Subject: RE: [PATCH v3] net:Add sysctl_max_skb_frags
Thread-Topic: [PATCH v3] net:Add sysctl_max_skb_frags
Thread-Index: AQHRXn0Ol1Ird1KLrUuwhdg1KBRNj58aktLA
Date: Wed, 3 Feb 2016 17:36:24 +0000
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From: Herbert Xu
> Sent: 03 February 2016 12:21
> On Wed, Feb 03, 2016 at 12:36:21PM +0100, Hannes Frederic Sowa wrote:
> >
> > Agreed that it feels like a hack, but a rather simple one. I would
> > consider this to be just a performance improvement. We certainly need
> > a slow-path when virtio drivers submit gso packets to the stack (and
> > already discussed with Hans). The sysctl can't help here. But without
> > the sysctl the packets would constantly hit the slow-path in case of
> > e.g. IPoIB and that would also be rather bad.
> 
> So you want to penalise every NIC in the system if just one of
> them is broken? This is insane.  Just do the partial linearisation
> in that one driver that needs it and not only won't you have to
> penalise anyone else but you still get the best result for that
> driver that needs it.
> 
> Besides, you have to implement the linearisation anyway because
> of virtualisation.

And if a MAC driver needs to linearize a tx frame it might as well
copy it into a separately allocated tx buffer area.
Indeed it can copy fragments until the number left is less than the
fragment limit.

	David