netdev - Re: tbf/htb qdisc limitations

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Date:	Wed, 20 Oct 2010 11:06:13 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Bill Fink <billfink@...dspring.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Rick Jones <rick.jones2@...com>,
	Steven Brudenell <steven.brudenell@...il.com>,
	netdev@...r.kernel.org
Subject: Re: tbf/htb qdisc limitations

On Tue, Oct 19, 2010 at 03:37:24AM -0400, Bill Fink wrote:
> On Sun, 17 Oct 2010, Jarek Poplawski wrote:
> 
> > On Sat, Oct 16, 2010 at 09:24:34PM -0400, Bill Fink wrote:
> > > On Sat, 16 Oct 2010, Jarek Poplawski wrote:
> > ...
> > > > http://code.google.com/p/pspacer/wiki/HTBon10GbE
> > > >  
> > > > If it doesn't help reconsider hfsc.
> > > 
> > > Thanks for the link.  From his results, it appears you can
> > > get better accuracy by keeping TSO/GSO enabled and upping
> > > the tc mtu parameter to 64000.  I will have to try that out.
> > 
> > Sure, but you have to remember that scheduler doesn't know real packet
> > sizes and rate tables are less accurate especially for smaller packets,
> > so it depends on conditions.
> 
> On my testing on the real data path, TSO/GSO enabled did seem
> to give more accurate results for a single stream.  But when
> I tried multiple 10-GigE paths simultaneously, each with a
> single stream across it, non-TSO/GSO seemed to fare better
> overall.

Btw, if you find time I would be interested in checking an opposite
concept of lower than real mtu (256) to use rate tables different way
(other tbf parameters without change). The patch below is needed for
this to work.

Thanks,
Jarek P.
---

diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index 641a30d..9ac3460 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -123,9 +123,6 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc* sch)
 	struct tbf_sched_data *q = qdisc_priv(sch);
 	int ret;
 
-	if (qdisc_pkt_len(skb) > q->max_size)
-		return qdisc_reshape_fail(skb, sch);
-
 	ret = qdisc_enqueue(skb, q->qdisc);
 	if (ret != NET_XMIT_SUCCESS) {
 		if (net_xmit_drop_count(ret))
--
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