netdev - Re: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs with TCQ_F

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Date:	Wed, 24 Sep 2014 12:22:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Florian Westphal <fw@...len.de>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Dave Taht <dave.taht@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs
 with TCQ_F_ONETXQUEUE

On Wed, 2014-09-24 at 11:34 -0700, Tom Herbert wrote:
> >
> I believe drivers typically use skb->len for BQL tracking. Since
> bytelimit is based on BQL here, it might be more correct to use
> skb->len.

That is only because drivers dont have access to qdisc_pkt_len(skb) as :

- We can call them without any qdisc traversal
- We escaped from qdisc layer, and gso packet do not have the field set

And drivers actually update BQL inflight, while bulk dequeue do not
update it (its a local copy)

I do not particularly care, as BQL do not have to be 100% precise.


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