netdev - Re: [RFC net-next PATCH V3 0/2] qdisc bulk dequeuing and utilizing delayed tailptr updates

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Date:	Fri, 19 Sep 2014 15:39:27 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Florian Westphal <fw@...len.de>,
	Daniel Borkmann <dborkman@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Alexander Duyck <alexander.duyck@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Dave Taht <dave.taht@...il.com>, toke@...e.dk
Subject: Re: [RFC net-next PATCH V3 0/2] qdisc bulk dequeuing and utilizing
 delayed tailptr updates

On Fri, Sep 19, 2014 at 2:45 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2014-09-19 at 23:31 +0200, Jesper Dangaard Brouer wrote:
>
>> How can I test if the dev supports BQL?
>
>
> CONFIG_BQL should be enough.

Then why commits like this one?

commit 7070ce0a6419a118842298bc967061ad6cea40db
Author: Alexander Duyck <alexander.h.duyck@...el.com>
Date:   Sat Sep 28 06:00:37 2013 +0000

    i40e: Add support for Tx byte queue limits

    Implement BQL (byte queue limit) support in i40e.


>
> If a device driver do nothing about BQL, byte_queue_limits/limit will be
> zero by default.

Also note that for some virtual device, BQL may make no sense at all,
at least veth doesn't even use a TX queue (I know it has tx-0 mostly for
qdisc). Perhaps all NETIF_F_LLTX ones?
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