netdev - Re: [net-next 03/12] i40e: Handle a single mss packet with more than 8 frags

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Message-ID: <1416236150.5102.8.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 17 Nov 2014 06:55:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	Serey Kong <serey.kong@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"nhorman@...hat.com" <nhorman@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>,
	"jogreene@...hat.com" <jogreene@...hat.com>,
	Shannon Nelson <shannon.nelson@...el.com>
Subject: Re: [net-next 03/12] i40e: Handle a single mss packet with more
 than 8 frags

On Mon, 2014-11-17 at 14:40 +0000, David Laight wrote:

> Not that one.
> IIRC is was done to reduce the number of fragments through xennet.
> 
> You really want to try to keep some of the old fragments, just adding
> new ones to merge short sections.
> 
> OTOH 8 fragments isn't enough if the MAC supports TSO (dunno if it does).

I40 is a 40Gb NIC, it supports TSO, obviously.

> The skb_linearize() is only likely to fail for TSO anyway.
> Or rather, if it can't allocate a 4k page you are already stuffed.

So far, nobody wrote the code for this.

Page frag are allocated from pages, so if you cannot allocate a 4k page,
this function has no guarantee to succeed no matter how hard you tried.

alloc_skb_with_frags() was already _much_ better than a single
allocation of order-5 page. But if you feel you can do better, why don't
you provide the code ?


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