Re: [aqm] Questioning each PIE heuristic

"Rong Pan (ropan)" <ropan@cisco.com> Wed, 29 March 2017 17:58 UTC

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From: "Rong Pan (ropan)" <ropan@cisco.com>
To: "Lautenschlaeger, Wolfram (Nokia - DE/Stuttgart)" <wolfram.lautenschlaeger@nokia-bell-labs.com>, Luca Muscariello <luca.muscariello@gmail.com>, "Bless, Roland (TM)" <roland.bless@kit.edu>
CC: tsvwg IETF list <tsvwg@ietf.org>, Fred Baker <fredbaker.ietf@gmail.com>, Bob Briscoe <ietf@bobbriscoe.net>, "De Schepper, Koen (Nokia - BE/Antwerp)" <koen.de_schepper@nokia-bell-labs.com>, Greg White <g.white@cablelabs.com>, Jonathan Morton <chromatix99@gmail.com>, AQM IETF list <aqm@ietf.org>, Preethi Natarajan <prenatar@cisco.com>
Thread-Topic: [aqm] Questioning each PIE heuristic
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Date: Wed, 29 Mar 2017 17:58:08 +0000
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Subject: Re: [aqm] Questioning each PIE heuristic
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We are not holding back queued packets when the link is idle. We stop dropping packets when the queue is shallow in order to avoid unnecessary drops that could cause TCP traffic to back off and stop sending traffic that will cause link idle.

Rong

From: "Lautenschlaeger, Wolfram (Nokia - DE/Stuttgart)" <wolfram.lautenschlaeger@nokia-bell-labs.com<mailto:wolfram.lautenschlaeger@nokia-bell-labs.com>>
Date: Wednesday, March 29, 2017 at 2:30 AM
To: Rong Pan <ropan@cisco.com<mailto:ropan@cisco.com>>, Luca Muscariello <luca.muscariello@gmail.com<mailto:luca.muscariello@gmail.com>>, "Bless, Roland (TM)" <roland.bless@kit.edu<mailto:roland.bless@kit.edu>>
Cc: tsvwg IETF list <tsvwg@ietf.org<mailto:tsvwg@ietf.org>>, Fred Baker <fredbaker.ietf@gmail.com<mailto:fredbaker.ietf@gmail.com>>, Bob Briscoe <ietf@bobbriscoe.net<mailto:ietf@bobbriscoe.net>>, "De Schepper, Koen (Nokia - BE/Antwerp)" <koen.de_schepper@nokia-bell-labs.com<mailto:koen.de_schepper@nokia-bell-labs.com>>, Greg White <g.white@cablelabs.com<mailto:g.white@cablelabs.com>>, Jonathan Morton <chromatix99@gmail.com<mailto:chromatix99@gmail.com>>, AQM IETF list <aqm@ietf.org<mailto:aqm@ietf.org>>, Preethi Natarajan <prenatar@cisco.com<mailto:prenatar@cisco.com>>
Subject: RE: [aqm] Questioning each PIE heuristic

To my understanding a proper operating AQM _is_ work-conserving. Packet drops occur, if any, when a reasonable queue is present. And as long as packets are present in the queue, the link runs at 100%. I cannot see any (AQM) mechanism that is holding back queued packets while the link is idle.

Wolfram


From: aqm [mailto:aqm-bounces@ietf.org] On Behalf Of Rong Pan (ropan)
Sent: Dienstag, 28. März 2017 16:17
To: Luca Muscariello <luca.muscariello@gmail.com<mailto:luca.muscariello@gmail.com>>; Bless, Roland (TM) <roland.bless@kit.edu<mailto:roland.bless@kit.edu>>
Cc: tsvwg IETF list <tsvwg@ietf.org<mailto:tsvwg@ietf.org>>; Fred Baker <fredbaker.ietf@gmail.com<mailto:fredbaker.ietf@gmail.com>>; Bob Briscoe <ietf@bobbriscoe.net<mailto:ietf@bobbriscoe.net>>; De Schepper, Koen (Nokia - BE/Antwerp) <koen.de_schepper@nokia-bell-labs.com<mailto:koen.de_schepper@nokia-bell-labs.com>>; Greg White <g.white@cablelabs.com<mailto:g.white@cablelabs.com>>; Jonathan Morton <chromatix99@gmail.com<mailto:chromatix99@gmail.com>>; AQM IETF list <aqm@ietf.org<mailto:aqm@ietf.org>>; Preethi Natarajan <prenatar@cisco.com<mailto:prenatar@cisco.com>>
Subject: Re: [aqm] Questioning each PIE heuristic

Sorry for causing the confusion in choosing the word "work-conserving". If we apply AQM and can not achieving 100% line rate, i.e. losing throughput, it is a big No No. Since we are dealing with TCP traffic, excess drops can cause TCP to back off too much and under-utilize the link.

Rong

From: Luca Muscariello <luca.muscariello@gmail.com<mailto:luca.muscariello@gmail.com>>
Date: Tuesday, March 28, 2017 at 8:48 AM
To: "Bless, Roland (TM)" <roland.bless@kit.edu<mailto:roland.bless@kit.edu>>
Cc: Fred Baker <fredbaker.ietf@gmail.com<mailto:fredbaker.ietf@gmail.com>>, Jonathan Morton <chromatix99@gmail.com<mailto:chromatix99@gmail.com>>, tsvwg IETF list <tsvwg@ietf.org<mailto:tsvwg@ietf.org>>, Bob Briscoe <ietf@bobbriscoe.net<mailto:ietf@bobbriscoe.net>>, "De Schepper, Koen (Koen)" <koen.de_schepper@nokia.com<mailto:koen.de_schepper@nokia.com>>, Rong Pan <ropan@cisco.com<mailto:ropan@cisco.com>>, Greg White <g.white@cablelabs.com<mailto:g.white@cablelabs.com>>, AQM IETF list <aqm@ietf.org<mailto:aqm@ietf.org>>, Preethi Natarajan <prenatar@cisco.com<mailto:prenatar@cisco.com>>
Subject: Re: [aqm] Questioning each PIE heuristic

Work conserving is supposed to be referring to the scheduler.
I'm not familiar with work-conservation when it refers to active queue management.
I'm not sure it is actually defined.

I can understand that an AQM can produce under utilization of the link, but that is
different to work conservation. Or is it maybe more subtle than that?

Luca

On Tue, Mar 28, 2017 at 1:48 PM, Bless, Roland (TM) <roland.bless@kit.edu<mailto:roland.bless@kit.edu>> wrote:
Hi,

Am 28.03.2017 um 13:39 schrieb Fred Baker:

> I'm not convinced I understand the definitions of "work conserving"
> and "non work conserving" in this context. A "work conserving"
> scheduling algorithm keeps an interface transmitting as long as there
> is data in the queue, while a non-work-conserving algorithm reduces
> the effective rate of the interface by spacing packets out.

+1 (that's also the definition I use, so I'm lost here too)

Regards,
 Roland

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