netdev - Re: [PATCH 1/1] net_sched: drr: warn when qdisc is not work conserving

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Date:	Thu, 12 Jun 2014 19:09:24 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Florian Westphal <fw@...len.de>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] net_sched: drr: warn when qdisc is not work conserving

On 12. Juni 2014 18:38:03 MESZ, Florian Westphal <fw@...len.de> wrote:
>Patrick McHardy <kaber@...sh.net> wrote:
>> On 11. Juni 2014 20:35:18 MESZ, Florian Westphal <fw@...len.de>
>wrote:
>> >The DRR scheduler requires that items on the active list are work
>> >conserving, i.e. do not hold on to skbs for throttling purposes,
>etc.
>> >Attaching e.g. tbf renders DRR useless because all other classes on
>the
>> >active list are delayed as well.
>> >
>> >So, warn users that this configuration won't work as expected; we
>> >already do this in couple of other qdiscs, see e.g.
>> 
>> Why don't prevent this during configuration time in the first place?
>> It doesn't work, a warning might trigger long after creating the
>broken
>> configuration and will more likely go unnoticed.
>
>That would be nice.
>
>But that would require some annotation of the qdiscs wheter they're
>wc or not, right?
>
>With such annotation, qdisc_graft() could refuse such request.
>
>Is that what you have in mind?

Exactly. Probably this needs to be determined during initialization since f.i. HFSC can work in both modes.

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