netstack: performance w/TCP-RACK on Windows about gvisor HOT 7 OPEN

Adding @nybidari, who knows more about RACK.

Interesting that this is Windows-only, as I wouldn't expect that to matter. Maybe something to do with timers (since RACK is time-based) is OS-dependent?

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Adding @nybidari, who knows more about RACK.

Interesting that this is Windows-only, as I wouldn't expect that to matter. Maybe something to do with timers (since RACK is time-based) is OS-dependent?

FWIW I have tested with higher resolution timing, but found no difference in the results:

err := windows.TimeBeginPeriod(1)
if err != nil {
	panic(err)
}

I just now realized that tcpip.TCPRACKStaticReoWnd and tcpip.TCPRACKNoDupTh are meant to mask on top of tcpip.TCPRACK, and they are unused anyway. So when I was using those values it was the same as no RACK. Removed that bit from the description.

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I don't think RACK does anything different on windows compared to other operating systems.
From my understanding, RACK performance can be lower than other congestion control algorithms in these cases:

1. Packets were reordered and RACK adjusts the reordering window. Lets say RACK detected a large reordering window.
   Now if the packets (after RACK adjusted the reordering window to a large value) were actually lost, then RACK waits till the reordering window timeout to detect the packet loss. To adjust the reorder window back to the initial value, RACK will wait for 16 loss recoveries. Other congestion control algorithms do not consider reordering at all and in this case they will enter only one loss recovery falsely.
2. RTOs: I don't know how, but may be there are more RTOs with RACK on windows.

These are just my speculations, the root cause can be something else also!
To debug further, would it be possible to get these TCP stats for with and without RACK on windows:
https://github.com/google/gvisor/blob/master/pkg/tcpip/tcpip.go#L2123-L2146 ?

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To debug further, would it be possible to get these TCP stats for with and without RACK on windows: https://github.com/google/gvisor/blob/master/pkg/tcpip/tcpip.go#L2123-L2146 ?

30 second throughput test

Windows Server 2022 No TCP-RACK ~80Mb/s:

2023/11/30 00:57:00 Retransmits: 3299 FastRecovery: 0 SACKRecovery: 52 TLPRecovery: 0 SlowStartRetransmits: 1653 FastRetransmit: 52 Timeouts: 10

Windows Server 2022 TCP-RACK ~8Mb/s:

2023/11/30 00:59:40 Retransmits: 1430 FastRecovery: 0 SACKRecovery: 690 TLPRecovery: 0 SlowStartRetransmits: 4 FastRetransmit: 687 Timeouts: 4

Ubuntu 22.04 No TCP-RACK ~90Mb/s:

2023/11/30 01:05:31 Retransmits: 4251 FastRecovery: 0 SACKRecovery: 66 TLPRecovery: 0 SlowStartRetransmits: 2690 FastRetransmit: 66 Timeouts: 15

Ubuntu 22.04 TCP-RACK ~80Mb/s:

2023/11/30 01:03:07 Retransmits: 2220 FastRecovery: 0 SACKRecovery: 64 TLPRecovery: 0 SlowStartRetransmits: 3 FastRetransmit: 64 Timeouts: 1

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A friendly reminder that this issue had no activity for 120 days.

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@nybidari any findings? Any reason to believe a more recent release would improve RACK on windows?

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No findings, and no features have targeted this specifically. Wish we had more bandwidth to investigate.

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