I have the same am335x-based system running with both 3.18.x and 5.4.x
(6.2.1 too) kernels. In the full setup the system handles 4x FT4232-H
chips.
# lsusb -t
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=musb-hdrc/1p, 480M
|__ Port 1: Dev 2, If 0, Class=, Driver=hub/4p, 480M
|__ Port 2: Dev 3, If 0, Class=, Driver=ftdi_sio, 480M
|__ Port 2: Dev 3, If 1, Class=, Driver=ftdi_sio, 480M
|__ Port 2: Dev 3, If 2, Class=, Driver=ftdi_sio, 480M
|__ Port 2: Dev 3, If 3, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 1, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 2, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 0, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 3, Class=, Driver=ftdi_sio, 480M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=musb-hdrc/1p, 480M
|__ Port 1: Dev 2, If 0, Class=, Driver=hub/4p, 480M
|__ Port 2: Dev 3, If 0, Class=, Driver=ftdi_sio, 480M
|__ Port 2: Dev 3, If 3, Class=, Driver=ftdi_sio, 480M
|__ Port 2: Dev 3, If 1, Class=, Driver=ftdi_sio, 480M
|__ Port 2: Dev 3, If 2, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 0, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 1, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 2, Class=, Driver=ftdi_sio, 480M
|__ Port 3: Dev 4, If 3, Class=, Driver=ftdi_sio, 480M
When I open all 16 serial ports with the LOW_LATENCY flag in the
latest kernels, the system performance drops dramatically. It is best
to watch via iperf3:
Kernel 6.2.1
16 serial ports closed: 90.2 Mbits/sec
16 serial ports opened without LOW_LATENCY: 88.3 Mbits/sec
16 serial ports opened with LOW_LATENCY: 12.1 Mbits/sec
Kernel: 3.18.1
16 serial ports closed: 61.1 Mbits/sec
16 serial ports opened without LOW_LATENCY: 53.7 Mbits/sec
16 serial ports opened with LOW_LATENCY: 37.2 Mbits/sec
Any idea why the performance drop is so big?
Regards,
Yegor
