netdev - Re: [RFC PATCH net-next] net: pktgen: packet bursting via skb->xmit

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Date:	Sat, 27 Sep 2014 13:43:10 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	netdev@...r.kernel.org, Amir Vadai <amirv@...lanox.com>,
	Or Gerlitz <or.gerlitz@...il.com>
Subject: Re: [RFC PATCH net-next] net: pktgen: packet bursting via
 skb->xmit_more

On Fri, 2014-09-26 at 00:42 -0700, Eric Dumazet wrote:

> By the way with this patch, I now reach 10 Mpps on mlx4 
> 
> base line : 5 Mpps
> 
> + skb->xmit_more and quick hack in pjtgen (spinlock/unlock per packet)
> -> 7 Mpps
> 
> + burst of 16 packets, no spinlock per packet -> 10 Mpps

With careful study of mlx4 driver to remove false sharing, I now get 14
Mpps.

(Note they have a special feature to 'inline' small packets in tx
descriptors : If this is used, max rate is lower, because cpu spend more
cycles to perform the copies)

I find worrying driver authors do not know how to properly use a ring
buffer, and do not place the producer and consumer indexes in separate
cache lines.



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