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.
>
next prev parent 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