General list for discussing Bufferbloat
 help / color / mirror / Atom feed
From: "Bless, Roland (TM)" <roland.bless@kit.edu>
To: Luca Muscariello <luca.muscariello@gmail.com>
Cc: Jonathan Morton <chromatix99@gmail.com>,
	bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Bloat] when does the CoDel part of fq_codel help in the real world?
Date: Tue, 27 Nov 2018 11:35:00 +0100	[thread overview]
Message-ID: <86b16a95-e47d-896b-9d43-69c65c52afc7@kit.edu> (raw)
In-Reply-To: <CAHx=1M6ymNZxyYTTZo-ss3HEsh8D9Zt9zUnFsMLEEsdKQtzMPg@mail.gmail.com>

Hi,

Am 27.11.18 um 11:29 schrieb Luca Muscariello:
> I have never said that you need to fill the buffer to the max size to
> get full capacity, which is an absurdity.

Yes, it's absurd, but that's what today's loss-based CC algorithms do.

> I said you need at least the BDP so that the queue never empties out.
> The link is fully utilized IFF the queue is never emptied.

I was also a bit imprecise: you'll need a BDP in flight, but
you don't need to fill the buffer at all. The latter sentence
is valid only in the direction: queue not empty -> link fully utilized.

Regards,
 Roland

> 
> 
> 
> On Tue 27 Nov 2018 at 11:26, Bless, Roland (TM) <roland.bless@kit.edu
> <mailto:roland.bless@kit.edu>> wrote:
> 
>     Hi Luca,
> 
>     Am 27.11.18 um 10:24 schrieb Luca Muscariello:
>     > A congestion controlled protocol such as TCP or others, including
>     QUIC,
>     > LEDBAT and so on
>     > need at least the BDP in the transmission queue to get full link
>     > efficiency, i.e. the queue never empties out.
> 
>     This is not true. There are congestion control algorithms
>     (e.g., TCP LoLa [1] or BBRv2) that can fully utilize the bottleneck link
>     capacity without filling the buffer to its maximum capacity. The BDP
>     rule of thumb basically stems from the older loss-based congestion
>     control variants that profit from the standing queue that they built
>     over time when they detect a loss:
>     while they back-off and stop sending, the queue keeps the bottleneck
>     output busy and you'll not see underutilization of the link. Moreover,
>     once you get good loss de-synchronization, the buffer size requirement
>     for multiple long-lived flows decreases.
> 
>     > This gives rule of thumbs to size buffers which is also very practical
>     > and thanks to flow isolation becomes very accurate.
> 
>     The positive effect of buffers is merely their role to absorb
>     short-term bursts (i.e., mismatch in arrival and departure rates)
>     instead of dropping packets. One does not need a big buffer to
>     fully utilize a link (with perfect knowledge you can keep the link
>     saturated even without a single packet waiting in the buffer).
>     Furthermore, large buffers (e.g., using the BDP rule of thumb)
>     are not useful/practical anymore at very high speed such as 100 Gbit/s:
>     memory is also quite costly at such high speeds...
> 
>     Regards,
>      Roland
> 
>     [1] M. Hock, F. Neumeister, M. Zitterbart, R. Bless.
>     TCP LoLa: Congestion Control for Low Latencies and High Throughput.
>     Local Computer Networks (LCN), 2017 IEEE 42nd Conference on, pp.
>     215-218, Singapore, Singapore, October 2017
>     http://doc.tm.kit.edu/2017-LCN-lola-paper-authors-copy.pdf
> 
>     > Which is: 
>     >
>     > 1) find a way to keep the number of backlogged flows at a
>     reasonable value. 
>     > This largely depends on the minimum fair rate an application may
>     need in
>     > the long term.
>     > We discussed a little bit of available mechanisms to achieve that
>     in the
>     > literature.
>     >
>     > 2) fix the largest RTT you want to serve at full utilization and size
>     > the buffer using BDP * N_backlogged.  
>     > Or the other way round: check how much memory you can use 
>     > in the router/line card/device and for a fixed N, compute the largest
>     > RTT you can serve at full utilization. 
>     >
>     > 3) there is still some memory to dimension for sparse flows in
>     addition
>     > to that, but this is not based on BDP. 
>     > It is just enough to compute the total utilization of sparse flows and
>     > use the same simple model Toke has used 
>     > to compute the (de)prioritization probability.
>     >
>     > This procedure would allow to size FQ_codel but also SFQ.
>     > It would be interesting to compare the two under this buffer sizing. 
>     > It would also be interesting to compare another mechanism that we have
>     > mentioned during the defense
>     > which is AFD + a sparse flow queue. Which is, BTW, already
>     available in
>     > Cisco nexus switches for data centres.
>     >
>     > I think that the the codel part would still provide the ECN feature,
>     > that all the others cannot have.
>     > However the others, the last one especially can be implemented in
>     > silicon with reasonable cost.
> 


  reply	other threads:[~2018-11-27 10:35 UTC|newest]

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-26 19:08 Pete Heist
2018-11-26 19:28 ` Neal Cardwell
2018-11-27 20:42   ` Dave Taht
2018-11-27 20:54     ` Toke Høiland-Jørgensen
2018-11-27 21:00       ` Dave Taht
2018-11-27 21:05         ` Toke Høiland-Jørgensen
2018-11-26 21:29 ` Jonathan Morton
2018-11-27  9:24   ` Luca Muscariello
2018-11-27 10:26     ` Bless, Roland (TM)
2018-11-27 10:29       ` Luca Muscariello
2018-11-27 10:35         ` Bless, Roland (TM) [this message]
2018-11-27 10:40           ` Luca Muscariello
2018-11-27 10:50             ` Mikael Abrahamsson
2018-11-27 11:01               ` Luca Muscariello
2018-11-27 11:21                 ` Mikael Abrahamsson
2018-11-27 12:17                   ` Jonathan Morton
2018-11-27 13:37                     ` Luca Muscariello
2018-11-27 13:49                       ` Mikael Abrahamsson
2018-11-27 14:07                         ` Luca Muscariello
2018-11-27 14:18                           ` Mikael Abrahamsson
2018-11-27 18:44                           ` Kathleen Nichols
2018-11-27 19:25                             ` Dave Taht
2018-11-27 21:57                             ` Roland Bless
2018-11-27 11:53                 ` Bless, Roland (TM)
2018-11-27 11:58                   ` Luca Muscariello
2018-11-27 12:22                     ` Bless, Roland (TM)
2018-11-27 11:06               ` Jonathan Morton
2018-11-27 11:07               ` Michael Welzl
2018-11-29  7:35               ` Dave Taht
2018-11-29 18:43                 ` Stephen Hemminger
2018-11-29 19:08                   ` Dave Taht
2018-11-30  5:51                   ` Mikael Abrahamsson
2018-11-30 19:02                     ` Dave Taht
2018-11-30 19:58                     ` Stephen Hemminger
2018-11-27 11:04             ` Michael Welzl
2018-11-27 12:48               ` Bless, Roland (TM)
2018-11-27 11:40             ` Bless, Roland (TM)
2018-11-27 11:43               ` Bless, Roland (TM)
2018-11-29  7:39               ` Dave Taht
2018-11-29  7:45                 ` Jonathan Morton
2018-11-29  7:54                   ` Dave Taht
2018-11-29  8:09                     ` Luca Muscariello
2018-11-29 13:49                   ` Bless, Roland (TM)
2018-11-29  8:41                 ` Bless, Roland (TM)
2018-11-29  7:33       ` Dave Taht
2018-11-29  8:13         ` Bless, Roland (TM)
2018-11-29 10:00         ` Pete Heist
2018-11-29 16:09       ` Luca Muscariello
2018-11-29 17:07         ` Mario Hock
2018-11-29 22:30           ` Luca Muscariello
2018-11-30  9:55             ` Mario Hock
2018-11-30 10:32               ` Luca Muscariello
2018-11-30 11:04                 ` Jonathan Morton
2018-11-30 11:53                   ` jf
2018-12-03  9:42                   ` Mario Hock
2018-11-27 11:52     ` Toke Høiland-Jørgensen
2018-11-28  3:37       ` [Bloat] AFD Dave Taht
2018-11-27 20:58     ` [Bloat] when does the CoDel part of fq_codel help in the real world? Dave Taht
2018-11-27 22:19       ` Luca Muscariello
2018-11-27 22:30         ` Roland Bless
2018-11-27 23:17           ` Dave Taht
2018-11-28  3:47             ` Kathleen Nichols
2018-11-28  9:56       ` Luca Muscariello
2018-11-28 10:40         ` Dave Taht
2018-11-28 10:48           ` Luca Muscariello
2018-11-28 12:10             ` Bless, Roland (TM)
2018-11-29  7:22               ` Dave Taht
2018-11-29  7:20             ` Dave Taht
2018-11-27 20:50   ` Dave Taht
2018-11-26 21:56 ` Michael Welzl
2018-11-26 22:13   ` Toke Høiland-Jørgensen
2018-11-27  8:54     ` Pete Heist
2018-11-27  9:31       ` Jonathan Morton
2018-11-27 13:19       ` Michael Richardson
2018-11-27 18:59         ` Jonathan Morton
2018-11-27 20:10   ` Dave Taht
2018-11-27 21:17     ` Michael Welzl
2018-11-27 21:20       ` Michael Welzl
2018-11-29  7:11         ` Dave Taht
2018-11-29  7:28           ` [Bloat] incremental deployment, transport and L4S (Re: when does the CoDel part of fq_codel help in the real world?) Mikael Abrahamsson
2018-11-29  7:36             ` Jonathan Morton
2018-11-29  7:46               ` Mikael Abrahamsson
2018-11-29  8:08                 ` Michael Welzl
2018-11-29 10:30                   ` Jonathan Morton
2018-11-29 12:06                     ` Michael Welzl
2018-11-29 12:52                       ` Jonathan Morton
2018-11-30  7:54                         ` Michael Welzl
2019-02-03 18:20                           ` Dave Taht
2018-11-29 12:12                   ` Michael Welzl
2018-11-29 12:56                     ` Jonathan Morton
2018-11-29 13:30                       ` Mikael Abrahamsson
2018-11-29 23:27                         ` Jonathan Morton
2018-11-30  6:01                           ` Mikael Abrahamsson
2018-11-29 14:06                     ` Bless, Roland (TM)
2018-11-29  8:09                 ` Jonathan Morton
2018-11-29  8:19                   ` Mikael Abrahamsson
2018-11-29  8:34                     ` Jonathan Morton
2018-11-29 10:15                 ` Sebastian Moeller
2018-11-29 10:53                   ` Mikael Abrahamsson
2018-11-30  4:54               ` Dave Taht
2018-11-28  2:04     ` [Bloat] when does the CoDel part of fq_codel help in the real world? Pete Heist
2018-11-28  3:52       ` Dave Taht

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: https://lists.bufferbloat.net/postorius/lists/bloat.lists.bufferbloat.net/

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=86b16a95-e47d-896b-9d43-69c65c52afc7@kit.edu \
    --to=roland.bless@kit.edu \
    --cc=bloat@lists.bufferbloat.net \
    --cc=chromatix99@gmail.com \
    --cc=luca.muscariello@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox