Major performance issues (Socketcan at 1K bit rate) #1135

Bug Description
More than half of the sent can frames are lost as the python code can't keep up.
5000 frames are being sent and candump has no difficulty receiving them. Python-can just can't.
Only receives 1270 out of the 5000.

To Reproduce
Two TCUs (ARM 800mhz) exchanging 5000 frames per second on 1mbps can wire.
Sender uses cangen can1 -n 5000 -g 0.0001
Receiver TCU as one very simple reception line and doesn't do anything except looping.

try:
    for msg in bus:
        if (cnt >= 5000):
            break
        cnt = cnt + 1
       
except KeyboardInterrupt:
    pass

Expected behavior
ECUs connected with a 1mbps bus can exchange up to 60k can frames... Using Python-can, we can't even "read" just 5000 frames !
Is this normal ?

Additional context

OS-version: Debian 10
Python version: Python 3.7.3
python-can version: 3.3.4
python-can interface/s: SocketCan