[tcpPrague] Queries about prague linux code

Deepak K <deepakkavoor99@gmail.com> Sat, 08 August 2020 17:39 UTC

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From: Deepak K <deepakkavoor99@gmail.com>
Date: Sat, 8 Aug 2020 23:08:41 +0530
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Subject: [tcpPrague] Queries about prague linux code
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Hello everyone,
Hope you're doing well. I had a couple of quick questions about the current
TCP Prague code at https://github.com/L4STeam/linux

1) There was a mention in Page 6 here (
https://www.bobbriscoe.net/projects/latency/tcp-prague-netdev0x13.pdf) that
if Prague encounters a packet loss while in CWR state, ssthresh would be
reduced by (2+alpha)/4 instead of the usual 50% reduction. However as far
as I understand, the current code reduces it by half irrespective of
whether it's in CWR. Is that right?

2) I have some questions with the flow of code when RTT scaling heuristic
is particularly set to RTT_CONTROL_ADDITIVE.
In prague_ai_ack_increase (), the function
rtt_scaling_ops->ai_ack_increase() is called, with the parameter srtt_us.
This in-turn calls prague_rate_scaled_ai_ack_increase() with the same
parameter value. Now, srtt_us is compared with the result of
prague_target_rtt(). This function maps to prague_dynamic_rtt_target(),
which returns ca->rtt_target + srtt_us.

So, doesn't this lead to a comparison between srtt_us and ca->rtt_target +
srtt_us, which is redundant?

Thanks!