Re: [tcpm] ACK aggregation and congestion window growth

Rick Jones <perfgeek@mac.com> Fri, 26 April 2019 14:03 UTC

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From: Rick Jones <perfgeek@mac.com>
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Date: Fri, 26 Apr 2019 07:03:06 -0700
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To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
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Subject: Re: [tcpm] ACK aggregation and congestion window growth
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Does your ACK aggregator also delay the ACKs of SYNchronize segments? If not, perhaps the congestion control sees the increase (?) in round trip time after connection establishment as a signal of congestion and behaves accordingly. 

> On Apr 26, 2019, at 06:46, Ingemar Johansson S <ingemar.s.johansson@ericsson.com>; wrote:
> 
> Hi
>  
> I am experimenting with a simple test setup with 2 Ubuntu 18.04 PCs (Cubic CC).
> Between these two I have a simple setup that aggregates ACKs so that they are forwarded to the server only every 10ms. The min RTT is 18ms.
> The problem I see is that even though I should reach 1Gbps throughput, I only get around 200Mbps.
> I would believe that the congestion window should eventually increase enough to handle the burstiness given by the ACK aggregation but it seems like this is not the case.
> Is there a limitation in the Linux stack that prevents congestion window growth when ACKs arrive in bursts like this ?
>  
> /Ingemar
> ==================================
> Ingemar Johansson  M.Sc.
> Master Researcher
>  
> Ericsson Research
> Network Protocols & E2E Performance
> Labratoriegränd 11
> 971 28, Luleå, Sweden
> Phone +46-1071 43042
> SMS/MMS +46-73 078 3289
> ingemar.s.johansson@ericsson.com
> www.ericsson.com
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