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From: David Lang <david@lang.hm>
To: Sebastian Moeller <moeller0@gmx.de>
Cc: Jonathan Morton <chromatix99@gmail.com>,
	"cake@lists.bufferbloat.net" <cake@lists.bufferbloat.net>
Subject: Re: [Cake] CAKE upstreaming - testers wanted, ACK filtering rescuers needed
Date: Thu, 26 Apr 2018 17:17:08 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.02.1804261715350.4538@nftneq.ynat.uz> (raw)
In-Reply-To: <51A5A6AB-4B1C-4795-8136-9EB63E59598B@gmx.de>

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1880 bytes --]

On Thu, 26 Apr 2018, Sebastian Moeller wrote:

>> On Apr 26, 2018, at 09:26, Jonathan Morton <chromatix99@gmail.com> wrote:
>> 
>>> Genuine question:  I have a superpacket circa 64K, this is a lump of data in a tcp flow.  I have another small VOIP packet, it’s latency sensitive.  If I split the super packet into individual 1.5K packets as they would be on the wire, I can insert my VOIP packet at suitable place in time such that jitter targets are not exceeded.  If I don’t split the super packet, surely I have to wait till the end of the superpacket’s queue (for want of a better word) and possibly exceed my latency target.  That looks to me like ‘GSO/TSO’ is potentially bad for interflow latencies.
>> 
>>> What don’t I understand here?
>> 
>> You have it exactly right.  For some reason, Eric is failing to consider the general case of flow-isolating queues at low link rates, and only considering high-rate FIFOs.
>> 
>> More to the point, at 64Kbps a maximal GSO packet can take 8 seconds to clear, while an MTU packet takes less than a quarter second!
>
> 	I venture a guess that it is not so much the concept but rather the 
> terminology that irritates Eric? If at all Superpackets lighten the kernel's 
> load and will in all likelihood make in-kernel processing faster which if at 
> all decreases latency. The effect on flow fairness that we are concerned about 
> might simply not register under "latency" for the kernel developers; I am sure 
> they see the issue and this is really about which words to use to describe 
> this... Also I point at the fact that Eric did not object to the feature per 
> se, but rather the unconditionality and the rationale.

Keep in mind that he was also griping about the focus on <100M bandwidth limits 
and talking about >10G links. At those speeds, the large GSO packet is not a 
significant factor.

David Lang

  parent reply	other threads:[~2018-04-27  0:17 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25 20:45 Toke Høiland-Jørgensen
2018-04-26  1:10 ` Ryan Mounce
2018-04-26  1:32   ` Stephen Hemminger
2018-04-26  3:23     ` Dave Taht
2018-04-26  6:39   ` Toke Høiland-Jørgensen
2018-04-26  6:54     ` Ryan Mounce
2018-04-26  7:14       ` Toke Høiland-Jørgensen
2018-04-26  7:19 ` Kevin Darbyshire-Bryant
2018-04-26  7:34   ` Toke Høiland-Jørgensen
2018-04-26  8:43     ` Jonas Mårtensson
2018-04-26  8:55       ` Toke Høiland-Jørgensen
2018-04-26 12:02         ` Jonas Mårtensson
     [not found] ` <mailman.301.1524727201.3573.cake@lists.bufferbloat.net>
2018-04-26  7:26   ` Jonathan Morton
2018-04-26  7:43     ` Sebastian Moeller
2018-04-26 14:42       ` Jonathan Morton
2018-04-26 15:25         ` Sebastian Moeller
2018-04-27  0:17       ` David Lang [this message]
2018-04-26  8:16     ` Kevin Darbyshire-Bryant

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