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Date:	Sun, 28 Sep 2014 11:52:44 -0700
From:	Eric Dumazet <>
To:	Alexei Starovoitov <>
Cc:	Or Gerlitz <>,
	"David S. Miller" <>,
	Jesper Dangaard Brouer <>,
	Eric Dumazet <>,
	John Fastabend <>,
	Linux Netdev List <>,
	Amir Vadai <>,
	Or Gerlitz <>
Subject: Re: [PATCH net-next] mlx4: optimize xmit path

On Sun, 2014-09-28 at 11:07 -0700, Alexei Starovoitov wrote:

> this is great improvement!
> Thank you for leading this effort.
> 10G line rate is definitely nice :)
> Hopefully Or can demo similar numbers with 40G nic as well :)
> > +       if (ring->bf_enabled && desc_size <= MAX_BF && !bounce &&
> > +           !vlan_tx_tag_present(skb) && send_doorbell) {
> feels something wrong here, since it checks for
> send_doorbell, but iowrite() happens in the 'else' part
> of this branch with another 'if (send_doorbell)'

If we do not plan to send a doorbell, we should not use blueframe.

Blueframe is always sending a doorbell by design, as it uses a single
flip buffer.

So if you want to see any improvement thanks to skb->xmit_more, we have
to use the iowrite32(), not the blueframe.

Therefore , if send_doorbell == false, we do not want the doorbell

Is it making sense now ? ;)

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