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rgbtxus Author

Level 1

4 points

Network speed

The question is about the TCP transfer speed between my 2021 MacBook Pro 16" M1 and my linux file server. Using iperf3 I measure 941 Mbit/sec moving data from the server to the Mac (ipref3 -c <ipaddr> -R) which is a fine result but only 236Mbit/sec from the MAC to the server (ipref3 -c <ipaddr>). This is ony 1/4 the speed and as this is the most common usage I would really like to find out why and fix it if possible. I assume it is a network setting on one of the machines. Can anyone shed some light on this??

I have tried various settings of net.inet.tcp.delayed_ack and net.inet.tcp.win_scale_factor on the MAC with no apparent result impact. I then tried the test from an older PC laptop and also experienced a large reduction in speed going from the laptop to the server v.s. the server to the laptop. This seems to suggest that the issue is with the linux tcp settings.

MacBook Pro (2020 and later)

Posted on Mar 24, 2022 7:53 AM

Top-ranking reply

rgbtxus Author

Level 1

4 points

Posted on Mar 24, 2022 8:44 AM

Replying to my own post -- it was the cable! I replaced it with a new CAT6 I had on the shelf and 236 jumped to 733. Not sure why I did not try replacing the cable before. I just did not consider that it would perfectly in one direct but not in the other!

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Network speed

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