netdev - Re: inaccurate packet scheduling

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Date:	Thu, 07 Feb 2013 09:47:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	edumazet@...gle.com, netdev@...r.kernel.org, kuznet@....inr.ac.ru,
	jhs@...atatu.com
Subject: Re: inaccurate packet scheduling

On Thu, 2013-02-07 at 18:39 +0100, Jiri Pirko wrote:
> Thu, Feb 07, 2013 at 05:39:35PM CET, eric.dumazet@...il.com wrote:
> >On Thu, 2013-02-07 at 17:13 +0100, Jiri Pirko wrote:
> >
> >> >I tried kernel with this patch in. I also ported
> >> >56b765b79e9a78dc7d3f8850ba5e5567205a3ecd to tbf. I'm getting always the
> >> >similar numbers with iperf. There must be something else needed :/
> >> 
> >> Any other ideas?
> >
> >You didn't post any patch, how can I comment on them ?
> 
> Okay, sorry, here it is. But as I said, it did not help.
> 
> Subject: [patch net-next RFC] tbf: improved accuracy at high rates
> 
> Current TBF uses rate table computed by the "tc" userspace program,
> which has the following issue:
> 
> The rate table has 256 entries to map packet lengths to
> token (time units).  With TSO sized packets, the 256 entry granularity
> leads to loss/gain of rate, making the token bucket inaccurate.
> 
> Thus, instead of relying on rate table, this patch explicitly computes
> the time and accounts for packet transmission times with nanosecond
> granularity.
> 
> This is a followup to 56b765b79e9a78dc7d3f8850ba5e5567205a3ecd
> 
> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
> ---

This patch doesnt change  q->max_size

So you hit this :

if (qdisc_pkt_len(skb) > q->max_size)
    return qdisc_reshape_fail(skb, sch);

I thought this point was already mentioned in my previous mails.



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