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Date:	Wed, 3 Feb 2016 17:36:24 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Herbert Xu' <>,
	Hannes Frederic Sowa <>
CC:	Hans Westgaard Ry <>,
	"David S. Miller" <>,
	Alexey Kuznetsov <>,
	James Morris <>,
	Hideaki YOSHIFUJI <>,
	"Patrick McHardy" <>,
	Tom Herbert <>,
	"Pablo Neira Ayuso" <>,
	Eric Dumazet <>,
	"Florian Westphal" <>, Jiri Pirko <>,
	Alexander Duyck <>,
	Michal Hocko <>,
	Linus Lüssing <>,
	Tejun Heo <>,
	Andrew Morton <>,
	Alexey Kodanev <>,
	Håkon Bugge <>,
	open list <>,
	"open list:NETWORKING [GENERAL]" <>
Subject: RE: [PATCH v3] net:Add sysctl_max_skb_frags

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.


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