Hello,
I am currently developing a headless macOS daemon (HarmonBridge) that requires extremely low-latency, high-bandwidth UDP video streaming between a Mac and a Linux host over a dedicated 2.5GbE/5GbE local network link.
We are utilizing widely available Realtek RTL8156 / RTL8156B based USB 2.5G network adapters. Under macOS, these adapters default to the generic com.apple.DriverKit.AppleUserECM driver. The hardware itself natively supports Jumbo Frames (MTU 9000), but the DriverKit implementation artificially restricts the MTU cap to 1500 bytes.
Because we are forced through MTU 1500, we are incurring significant performance penalties:
Excessive IP fragmentation for our large UDP video payloads. Unnecessary CPU overhead due to increased hardware interrupts and header processing at 2.5Gbps speeds. For a latency-critical application like ours, reducing CPU interrupts and utilizing true hardware-level Jumbo Frames is essential.
My Questions:
Is there an undocumented boot-arg or network sysctl parameter that permits overriding the AppleUserECM 1500 MTU hard-limit for 2.5G USB adapters on Apple Silicon? Are there any roadmap plans from the DriverKit/Networking team to re-enable standard Jumbo Frame negotiation for RTL8156 hardware using the generic ECM driver? If the answer to both is no, does Apple grant NetworkingDriverKit Entitlements to independent developers specifically for the purpose of writing custom hardware overrides to patch missing MTU features in the default ECM stack? Because AppleUserECM effectively acts as a gatekeeper to the underlying MAC/PHY capabilities of these modern USB NICs, any guidance on achieving wire-native MTU 9000 under the current DriverKit paradigm would be hugely appreciated.
Thank you!