From: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
To: <cake@lists.bufferbloat.net>
Subject: Re: [Cake] Running Cake at long RTTs
Date: Fri, 30 Oct 2015 20:30:29 +0000 [thread overview]
Message-ID: <5633D365.1060004@darbyshire-bryant.me.uk> (raw)
In-Reply-To: <5632591A.5040403@darbyshire-bryant.me.uk>
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On 29/10/15 17:36, Kevin Darbyshire-Bryant wrote:
>
> On 27/10/15 15:14, Toke Høiland-Jørgensen wrote:
>> So Dave and I did a bit of testing of Cake at a 1-second base RTT. That
>> showed that, compared with a straight FIFO queue (with a sufficiently
>> large buffer), throughput was suffering quite a bit under Cake,
>> especially at large bandwidths. We did two changes to fix this:
>>
>> - Turn the hard packet queue size into a lower bound rather than an
>> upper bound.
>>
>> - Scale the target to be 1/16th of the interval.
>>
>> The first change allows Cake to actually reach the target throughput,
>> but it still takes a long while to get there. With the second change, we
>> actually get the desired behaviour. The attached plot shows the
>> difference, with the solid line being before the change and the dashed
>> line being after the change.
>>
>> Patch attached.
>>
>> -Toke
> That patch is really going to behave strangely indeed. You end up with
> b->cparams.interval = max(rtt_est_ns + b->cparams.target -
> ns_target,b->cparams.target * 8);
> b->cparams.target = max(max(byte_target_ns, ns_target),
> b->cparams.interval >> 4);
>
> So interval no matter what happens takes note of 'cparams.target' which
> hasn't yet been set (on first run is 0)
> And target wants to take interval/16, which may be based on the previous
> calculation. Erm. Needs more thought.
>
> My brain isn't working at the moment due to illness, but recursively
> playing with bandwidth settings on cake is most entertaining at the
> moment ;-)
>
> Kevin (dead with cold/high as a kite on cold drugs)
Right, I've just pushed a slightly uncomfortable fix for this but it
does at least make cake behave in a deterministic manner again.
>
>
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next prev parent reply other threads:[~2015-10-30 20:30 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-27 15:14 Toke Høiland-Jørgensen
2015-10-27 15:16 ` Loganaden Velvindron
[not found] ` <6499FF74-D13B-4B2E-90E3-D1FDD3FD1468@gmx.de>
2015-10-27 16:50 ` Toke Høiland-Jørgensen
2015-10-27 17:14 ` Sebastian Moeller
2015-10-27 19:04 ` Jonathan Morton
2015-10-27 23:57 ` Toke Høiland-Jørgensen
2015-10-28 9:36 ` Sebastian Moeller
2015-10-28 15:28 ` Sebastian Moeller
2015-10-28 15:36 ` Toke Høiland-Jørgensen
2015-10-28 15:50 ` Sebastian Moeller
2015-10-28 16:34 ` Toke Høiland-Jørgensen
2015-10-28 17:44 ` Sebastian Moeller
2015-10-29 17:36 ` Kevin Darbyshire-Bryant
2015-10-30 20:30 ` Kevin Darbyshire-Bryant [this message]
2015-10-30 21:34 ` Dave Taht
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