Input lag of eGPUs

[thanossapiens]

Do external GPUs always introduce input lag?
I found only one post about it https://shaneycg.github.io/razer-core-latency/, have there been any other tests?
There does seem to be lag if the signal is resent to the device instead of an external display.

[Chief Blur Buster]

Do external GPUs always introduce input lag?
I found only one post about it https://shaneycg.github.io/razer-core-latency/, have there been any other tests?
There does seem to be lag if the signal is resent to the device instead of an external display.

There can be indeed latency from the extra frame-transmission overheads. Transmission of uncompressed frames over ThunderBolt would be dependent on the resolution. An uncompressed 1080p 24-bit frame is 6 megabytes, and transferring (including overheads) probably takes about a millisecond in real-world USB-C / Thunderbolt 3 transmission.

There may be additional driver overheads. Best case would probably be something like under half a millisecond but could be as bad as a few millisecond (2-3ms) -- someone would need to test this. At high frame rates like 200 frames per second, the frame transmission overhead can become quite significant.

You've got lots of 2-way traffic with an eGPU, like texture transmission and then the backchannel of sending back completed frames for display on the internal display.