netdev - Re: Question on bulk dequeue support in virtual drivers

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Date:	Thu, 20 Nov 2014 07:26:28 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	James Yonan <james@...nvpn.net>
Cc:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: Question on bulk dequeue support in virtual drivers

On Thu, 2014-11-20 at 05:39 -0700, James Yonan wrote:
> Consider a tunneling driver that receives packets in ndo_start_xmit, 
> encapsulates them in UDP, and forwards via ip_local_out.  The 
> ndo_start_xmit implementation can implement bulking by looking at 
> skb->xmit_more.  But then how to efficiently transmit the resulting 
> bulked list of encapsulated packets via UDP, so that the packets both 
> enter and leave the driver in bulked form?  Is there an ip_local_out 
> alternative for bulked skb lists?

There is no such thing. Quite frankly it wont happen. Consider IP stacks
and netfilter, there is no provision for batches (other than GSO/TSO)

xmit_more addresses a specific hardware problem, it is not an
alternative for batches.

xmit_more will happen in your case in the last step, from qdisc to
ethernet device.



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