netdev - Re: [PATCH take 2] pkt_sched: Fix qdisc_watchdog() vs. dev

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Message-ID: <20080924082810.GB4838@ff.dom.local>
Date:	Wed, 24 Sep 2008 08:28:10 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	kaber@...sh.net, alexander.h.duyck@...el.com
Subject: Re: [PATCH take 2] pkt_sched: Fix qdisc_watchdog() vs.
	dev_deactivate() race

On Wed, Sep 24, 2008 at 04:04:27PM +0800, Herbert Xu wrote:
> On Wed, Sep 24, 2008 at 07:15:21AM +0000, Jarek Poplawski wrote:
> >
> > > Then each qdisc can decide which child to recursively dequeue
> > > based on that token (or ignore it for non-prio qdiscs such as
> > > HTB).
> > 
> > I don't think HTB could be considered as a non-prio qdisc.
> 
> It is non-prio in the sense that it has other criteria for deciding
> which child qdisc to enqueue into.
> 
> > As matter of fact I can't figure out this idea of a prio at the root
> > or leaf either. Could you explain in which point do you expect the
> > gain? If it's about the locks, what kind of synchronization would be
> > used to assure packets from lower prio queues (or qdiscs?)  aren't
> > sent to free tx queues, while higher prio wait on stopped ones?
> 
> It's very simple really.  For a non-leaf prio you determine which
> child qdisc to enqueue into using the priority.  For a leaf prio
> you determine which software queue to enqueue into based on the
> priority.

OK, it's too simple then. Could you make this more complex and
show me the gain.

> To put it another way, what I'm saying is that instead of duplicating
> the qdiscs as we do now for pfifo_fast, we should make the leaf
> qdiscs duplicate its software queues to match the hardware queues
> it's feeding into.

It looks like sch_multiq, but you probably mean something else...

Cheers,
Jarek P.
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