netdev - Re: [PATCH 0/2] Get rid of ndo_xmit

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Date:	Wed, 27 Aug 2014 13:43:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	brouer@...hat.com
Cc:	netdev@...r.kernel.org, therbert@...gle.com, jhs@...atatu.com,
	hannes@...essinduktion.org, edumazet@...gle.com,
	jeffrey.t.kirsher@...el.com, rusty@...tcorp.com.au,
	dborkman@...hat.com
Subject: Re: [PATCH 0/2] Get rid of ndo_xmit_flush

From: Jesper Dangaard Brouer <brouer@...hat.com>
Date: Wed, 27 Aug 2014 14:19:18 +0200

> On Mon, 25 Aug 2014 16:34:58 -0700 (PDT)
> David Miller <davem@...emloft.net> wrote:
> 
>> Given Jesper's performance numbers, it's not the way to go.
>> 
>> Instead, go with a signalling scheme via new boolean skb->xmit_more.
>> 
>> This has several advantages:
>> 
>> 1) Nearly trivial driver support, just protect the tail pointer
>>    update with the skb->xmit_more check.
>> 
>> 2) No extra indirect calls in the non-deferral cases.
> 
> Even-though it is obvious that this new API skb->xmit_more will not
> hurt performance, especially given skb->xmit_more is always 0 in this
> kernel, I've still run my pktgen performance tests.
> 
> Compared to baseline[1]: (averaged 5609929 pps) (details below signature)
>  * (1/5609929*10^9)-(1/5603728*10^9) = -0.197ns
> 
> As expected, this API does not hurt performance (as -0.197ns is below
> our accuracy levels).
> 
> [1] http://thread.gmane.org/gmane.linux.network/327254/focus=327838

Thanks for validating Jesper :-)
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