Re: [aqm] ping loss "considered harmful"

Andrew Mcgregor <andrewmcgr@google.com> Mon, 02 March 2015 04:00 UTC

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Date: Mon, 2 Mar 2015 15:00:40 +1100
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From: Andrew Mcgregor <andrewmcgr@google.com>
To: Dave Taht <dave.taht@gmail.com>
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Cc: "aqm@ietf.org" <aqm@ietf.org>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>, bloat <bloat@lists.bufferbloat.net>
Subject: Re: [aqm] ping loss "considered harmful"
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Hash all pings into one fq_codel bucket reserved for the purpose, so if
we're getting DoSed we drop them, otherwise if they stay thin they get
prioritised?

On 2 March 2015 at 14:57, Dave Taht <dave.taht@gmail.com> wrote:

> On this thread over here, an otherwise pretty clueful user chose
> openwrt's qos-scripts over the sqm-scripts, because sqm-scripts had
> *higher ping loss*.
>
>
> http://forums.dlink.com/index.php?topic=61634.msg251125#msg251125
>
> (I note that both fq_codel enabled QoS systems outperformed
> streamboost by a lot, which I am happy about)
>
> wow. It never registered to me that users might make a value judgement
> based on the amount of ping loss, and in looking back in time, I can
> think of multiple people that have said things based on their
> perception that losing pings was bad, and that sqm-scripts was "worse
> than something else because of it."
>
> sqm-scripts explicitly *deprioritizes* ping. In particular, this
> reduces the impact of ping floods from ipv6 to your entire /64, or to
> your whole ipv4, fairly well. And I had made the point that
> prioritizing ping was a bad idea here (including some dripping sarcasm
> later in the piece).
>
> http://www.bufferbloat.net/projects/cerowrt/wiki/Wondershaper_Must_Die
>
> but wow, it never occurred to me - in all these years - that ping was
> the next core metric on simple tests. I can be really dumb.
>
> I use netperf-wrapper and tend to ignore most of the ping data, but
> certainly on some benchmarks we have published ping doesn't look as
> good as the other stuff, *because it is deprioritized below all the
> other traffic*. Not strictly rate limited - as some systems do by
> default, including openwrt, which is impossible to get right - just
> deprioritized....
>
> How can we fix this user perception, short of re-prioritizing ping in
> sqm-scripts?
>
> --
> Dave Täht
> Let's make wifi fast, less jittery and reliable again!
>
> https://plus.google.com/u/0/107942175615993706558/posts/TVX3o84jjmb
>
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-- 
Andrew McGregor | SRE | andrewmcgr@google.com | +61 4 1071 2221