netdev - Re: [net-next PATCH] dql: add a burst attribute

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Date:	Tue, 30 Sep 2014 07:26:35 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Florian Westphal <fw@...len.de>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	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 Høiland-Jørgensen <toke@...e.dk>
Subject: Re: [net-next PATCH] dql: add a burst attribute

On Tue, Sep 30, 2014 at 7:17 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2014-09-30 at 15:46 +0200, Florian Westphal wrote:
>> Eric Dumazet <eric.dumazet@...il.com> wrote:
>> > From: Eric Dumazet <edumazet@...gle.com>
>> >
>> > Add a new dql attribute, to control how much packets we are allowed to
>> > burst from qdisc to device.
>>
>> I understand the motivation for this, but I find it a bit out-of-place
>> to have a 'packet' type counter in bql context?
>>
>> Would it perhaps make more sense to restrict bulk dequeues by an upper
>> (possibly changeable from userspace) byte counter limit?
>
> The byte count is already provided : its the BQL limit.
> We already have ways to tune it (limit_min & limit_max)
> We do not think we need something else here.
> That was the whole point of reusing BQL in the first place : Its already
> powerful and implemented.
>
> This new attribute is a packet burst.
>
Yes, this is the wrong place to put it. DQL knows nothing about
packets or technically even bytes, it's a generic library that deal
with "objects" on a queue. I don't see how burst relates to this.

I would infer from the patch that what you want is to add an attribute
to the TX queue. Why not do this directly?

>
> When I suggested 'pburst' attribute for pktgen to Alexei, he sent a
> patch with "burst". Nobody complained.
>
> Now I am reusing what apparently was OK for pktgen, you seem to object.
>
> If you feel not comfortable with "burst", rename it to whatever you
> think is best.
>
> But please, do not hard code magic 7 in your code.
>
> Thanks
>
>
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