netdev - Re: [RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi

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Date:	Wed, 19 Aug 2015 15:07:09 +0000
From:	"Grumbach, Emmanuel" <emmanuel.grumbach@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"ido@...ery.com" <ido@...ery.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi

Hi Eric,

First, thank you a lot for your comments.

On 08/19/2015 05:14 PM, Eric Dumazet wrote:
> On Wed, 2015-08-19 at 15:59 +0300, Emmanuel Grumbach wrote:
> 
>> We could have enabled A-MSDU based on xmit-more, but the
>> rationale of using LSO is that when using pfifo-fast,
>> the Qdisc gets one packet and dequeues is straight away
>> which limits the possibility to get a lot of packets at
>> once. (Am I right here?).
> 
> No, you are not ;)
> 
> Key point for xmit_more is BQL being implemented in your driver.
> 
> Relevant code is in try_bulk_dequeue_skb()
> 

I'll look at it.
I was almost starting to implement that but then I thought with another
(good?) reason to use LSO. LSO gives me the guarantee that the packet is
directed to one peer, which might not be the case with xmit_more since
we have one Qdisc for several clients in case we are in AP mode.
Building an A-MSDU for several clients is not possible, at least not for
several client in the L2 (different MAC addresses).
LSO avoids this problem completely.
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