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Date:	Sun, 28 Sep 2014 13:49:21 -0700
From:	Alexei Starovoitov <>
To:	Eric Dumazet <>
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, Sep 28, 2014 at 11:52 AM, Eric Dumazet <> wrote:
> 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

I see. So xmit_more=true overrides blueflame=on settings.
I wonder what is the performance difference bf=on vs bf=off,
also whether a burst of N packets via bf is slower than
burst via queue+doorbell.
Some fun exploration for driver experts :)

> Is it making sense now ? ;)

It did, but only after studying this BlueFlame thingy ;)

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