netdev - Re: inaccurate packet scheduling

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Date:	Thu, 7 Feb 2013 19:56:18 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	edumazet@...gle.com, netdev@...r.kernel.org, kuznet@....inr.ac.ru,
	jhs@...atatu.com
Subject: Re: inaccurate packet scheduling

Thu, Feb 07, 2013 at 06:47:38PM CET, eric.dumazet@...il.com wrote:
>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.

Right. I think I get it now. the RFC patch I posted enables possibility
to remove the max_size limitation, right?

I'm not really familliar in this area so I had to stare at the code for
a while.

>
>
>
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