netdev - Re: Re: Re: Re: Re: [bisected regression] e1000e: "Detected Hardware Unit Hang"

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Message-ID: <1421346289.11734.82.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 15 Jan 2015 10:24:49 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Jarosch <thomas.jarosch@...ra2net.com>
Cc:	'Linux Netdev List' <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	e1000-devel <e1000-devel@...ts.sourceforge.net>
Subject: Re: Re: Re: Re: Re: [bisected regression] e1000e: "Detected
 Hardware Unit Hang"

On Thu, 2015-01-15 at 18:37 +0100, Thomas Jarosch wrote:
> On Thursday, 15. January 2015 09:20:37 Eric Dumazet wrote:
> > > for the sake of completeness:
> > > 1: hang
> > 
> > This is weird : This should have same effect then GRO off (at most one
> > segment per packet)
> 
> I thought so, too. OTOH the code path was changed from
> "goto merge" to "return -E2BIG". I didn't look at the code
> what happens at the "merge" label.

If you leave the "goto merge", then GRO still builds big GRO packets,
using a linked list of packets.

Then because drivers do not generally support NETIF_F_FRAGLIST,
core networking code linearizes such GRO packets before reaching
ndo_start_xmit()

Check 8a29111c7ca68d928dfab58636f3f6acf0ac04f7 "net: gro: allow to build
full sized skb" for details about this.



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