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

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Date:	Fri, 26 Sep 2014 08:44:30 -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
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:
> On Thu, 2014-09-25 at 18:20 -0700, Eric Dumazet wrote:
> > On Thu, 2014-09-25 at 17:46 -0700, Alexei Starovoitov wrote:
> > > This patch demonstrates the effect of delaying update of HW tailptr.
> > > (based on earlier patch by Jesper)
> > > 
> > > burst=1 is a default. It sends one packet with xmit_more=false
> > > burst=2 sends one packet with xmit_more=true and
> > >         2nd copy of the same packet with xmit_more=false
> > > burst=3 sends two copies of the same packet with xmit_more=true and
> > >         3rd copy with xmit_more=false
> > 
> > > 
> > > Cc: Jesper Dangaard Brouer <brouer@...hat.com>
> > > Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>
> > > ---
> > 
> > Perfect, this is what I had in mind, thanks !
> > 
> > Acked-by: Eric Dumazet <edumazet@...gle.com>
> > 
> 
> By the way with this patch, I now reach 10 Mpps on mlx4 

On the other hand, bnx2x is not that happy

[  381.424736] bnx2x: [bnx2x_start_xmit:3772(eth0)]BUG! Tx ring full
when queue awake!
[  381.432660] bnx2x: [bnx2x_start_xmit:3772(eth0)]BUG! Tx ring full
when queue awake!
[  381.440337] bnx2x: [bnx2x_start_xmit:3772(eth0)]BUG! Tx ring full
when queue awake!
[  381.448255] bnx2x: [bnx2x_start_xmit:3772(eth0)]BUG! Tx ring full
when queue awake!

When TX_BUSY is replied, and/or  netif_tx_stop_queue(txq) was done by
the driver, the 'burst' loop should stop

So your :

	if (more)
		goto xmit_more;

Should instead be :

	if (more && !netif_xmit_frozen_or_drv_stopped(txq))
		goto xmit_more;



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