netdev - Re: [PATCH net-next] mlx4: exploit skb->xmit_more to conditionally send doorbell

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Date:	Thu, 25 Sep 2014 08:06:55 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>,
	John Fastabend <john.r.fastabend@...el.com>
Subject: Re: [PATCH net-next] mlx4: exploit skb->xmit_more to conditionally
 send doorbell

On Thu, 2014-09-25 at 16:43 +0200, Jesper Dangaard Brouer wrote:
> On Thu, 25 Sep 2014 07:17:49 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > Tested with a modified pktgen version, I got a 40% increase of
> > throughput.
> 
> Pktgen is artificial benchmarking, you know ;-) :-P
> 
> If you really must use pktgen for this, you can use an unmodified
> pktgen against the qdisc layer by adding a VLAN interface on-top of the
> device you want to test.  I blame John, for telling me this ;-)
> 
> /me running away


But... Nothing yet in qdisc layer sets xmit_more, unless TSO is
disabled, and a GSO packet is segmented.

So you might notice some improvement with this patch, but not if you use
TSO, and a 40GB NIC is better with TSO on you know ;)



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