From: Nandita Dukkipati <nanditad@google.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Tomas Hruby <thruby@google.com>, netdev <netdev@vger.kernel.org>,
codel@lists.bufferbloat.net
Subject: Re: [Codel] [RFC v2] fq_codel : interval servo on hosts
Date: Tue, 4 Sep 2012 08:10:36 -0700 [thread overview]
Message-ID: <CAB_+Fg5xPRqEZNdH0mYogmm4LitMvycSLB-X1_7ryn4RY9FvSA@mail.gmail.com> (raw)
In-Reply-To: <1346503884.7996.65.camel@edumazet-glaptop>
The idea of using srtt as interval makes sense to me if alongside we
also hash flows with similar RTTs into same bucket. But with just the
change in interval, I am not sure how codel is expected to behave.
My understanding is: the interval (usually set to worst case expected
RTT) is used to measure the standing queue or the "bad" queue. Suppose
1ms and 100ms RTT flows get hashed to same bucket, then the interval
with this patch will flip flop between 1ms and 100ms. How is this
expected to measure a standing queue? In fact I think the 1ms flow may
land up measuring the burstiness or the "good" queue created by the
long RTT flows, and this isn't desirable.
On Sat, Sep 1, 2012 at 5:51 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Fri, 2012-08-31 at 18:37 -0700, Yuchung Cheng wrote:
>
>> Just curious: tp->srtt is a very rough estimator, e.g., Delayed-ACks
>> can easily add 40 - 200ms fuzziness. Will this affect short flows?
>
> Good point
>
> Delayed acks shouldnt matter, because they happen when flow had been
> idle for a while.
>
> I guess we should clamp the srtt to the default interval
>
> if (srtt)
> q->cparams.interval = min(tcp_srtt_to_codel(srtt),
> q->default_interval);
>
>
>
next prev parent reply other threads:[~2012-09-04 15:10 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-31 6:55 [Codel] fq_codel : interval servo Eric Dumazet
2012-08-31 13:41 ` Jim Gettys
2012-08-31 13:50 ` [Codel] [RFC] fq_codel : interval servo on hosts Eric Dumazet
2012-08-31 13:57 ` [Codel] [RFC v2] " Eric Dumazet
2012-09-01 1:37 ` Yuchung Cheng
2012-09-01 12:51 ` Eric Dumazet
2012-09-04 15:10 ` Nandita Dukkipati [this message]
2012-09-04 15:25 ` Jonathan Morton
2012-09-04 15:39 ` Eric Dumazet
2012-09-04 15:34 ` Eric Dumazet
2012-09-04 16:40 ` Dave Taht
2012-09-04 16:54 ` Eric Dumazet
2012-09-04 16:57 ` Eric Dumazet
2012-08-31 15:53 ` [Codel] fq_codel : interval servo Rick Jones
2012-08-31 16:23 ` Eric Dumazet
2012-08-31 16:59 ` Dave Taht
2012-09-01 12:53 ` Eric Dumazet
2012-09-02 18:08 ` Dave Taht
2012-09-02 18:17 ` Dave Taht
2012-09-02 23:28 ` Eric Dumazet
2012-09-02 23:23 ` Eric Dumazet
2012-09-03 0:18 ` Dave Taht
2012-08-31 16:40 ` Jim Gettys
2012-08-31 16:49 ` Jonathan Morton
2012-08-31 17:15 ` Jim Gettys
2012-08-31 17:31 ` Rick Jones
2012-08-31 17:44 ` Jim Gettys
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