Wolfram,
Just to explain some context. The PIE algorithm determines a dropping
probability at sample times (default 16ms), then continues to drop with
that probability until the next sample. If the queue had been large then
traffic ends, while the queue is draining towards zero it is still
dropping at the last calculated probability. So the PIE code includes a
heuristic that suppresses any drop if the queue is less than half the
target. Nonetheless, the PIE algo continues to calculate what the drop
probability /would/ be if a queue of more than half the target appeared
again.
This is so that the drop probability reflects a longer running measure
of the load as well as the instantaneous queue.
Bob
On 29/03/17 18:58, Rong Pan (ropan) wrote:
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)"
<[email protected]
<mailto:[email protected]>>
Date: Wednesday, March 29, 2017 at 2:30 AM
To: Rong Pan <[email protected] <mailto:[email protected]>>, Luca
Muscariello <[email protected]
<mailto:[email protected]>>, "Bless, Roland (TM)"
<[email protected] <mailto:[email protected]>>
Cc: tsvwg IETF list <[email protected] <mailto:[email protected]>>, Fred
Baker <[email protected] <mailto:[email protected]>>,
Bob Briscoe <[email protected] <mailto:[email protected]>>, "De
Schepper, Koen (Nokia - BE/Antwerp)"
<[email protected]
<mailto:[email protected]>>, Greg White
<[email protected] <mailto:[email protected]>>, Jonathan
Morton <[email protected] <mailto:[email protected]>>, AQM
IETF list <[email protected] <mailto:[email protected]>>, Preethi Natarajan
<[email protected] <mailto:[email protected]>>
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:[email protected]] *On Behalf Of *Rong Pan (ropan)
*Sent:* Dienstag, 28. März 2017 16:17
*To:* Luca Muscariello <[email protected]
<mailto:[email protected]>>; Bless, Roland (TM)
<[email protected] <mailto:[email protected]>>
*Cc:* tsvwg IETF list <[email protected] <mailto:[email protected]>>; Fred
Baker <[email protected] <mailto:[email protected]>>;
Bob Briscoe <[email protected] <mailto:[email protected]>>; De
Schepper, Koen (Nokia - BE/Antwerp)
<[email protected]
<mailto:[email protected]>>; Greg White
<[email protected] <mailto:[email protected]>>; Jonathan
Morton <[email protected] <mailto:[email protected]>>; AQM
IETF list <[email protected] <mailto:[email protected]>>; Preethi Natarajan
<[email protected] <mailto:[email protected]>>
*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 <[email protected]
<mailto:[email protected]>>
*Date: *Tuesday, March 28, 2017 at 8:48 AM
*To: *"Bless, Roland (TM)" <[email protected]
<mailto:[email protected]>>
*Cc: *Fred Baker <[email protected]
<mailto:[email protected]>>, Jonathan Morton
<[email protected] <mailto:[email protected]>>, tsvwg IETF
list <[email protected] <mailto:[email protected]>>, Bob Briscoe
<[email protected] <mailto:[email protected]>>, "De Schepper, Koen
(Koen)" <[email protected]
<mailto:[email protected]>>, Rong Pan <[email protected]
<mailto:[email protected]>>, Greg White <[email protected]
<mailto:[email protected]>>, AQM IETF list <[email protected]
<mailto:[email protected]>>, Preethi Natarajan <[email protected]
<mailto:[email protected]>>
*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)
<[email protected] <mailto:[email protected]>> 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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