I experienced very slow WiFi network on Linux, while my iPhone seems surf the Internet quit fast. I pinged a site and the RTT is more than 1000ms! There must be something wrong with my Linux configuration.
I tried to change the MTU from "Automatic" to "1400" on my Linux box. Surprisingly, it fix the problem. The RTT through ping drops to <100 ms.
I am not quite sure what’s the reason that changing the MTU makes the WiFi faster on Linux. That is possibly related to the WiFi NIC driver, or the network transportation, or the WiFi router, or something else. Anyway, it worth a try when experiencing slow WiFi network on Linux. The MTU should not always be "1400" — some numbers larger than it may work better.