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

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Message-ID: <20140612163803.GD1982@breakpoint.cc>
Date:	Thu, 12 Jun 2014 18:38:03 +0200
From:	Florian Westphal <fw@...len.de>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] net_sched: drr: warn when qdisc is not work
 conserving

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?
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