UART has lag with low baud rate

There is a lag in the UART as shown in the thread below.

It’s like the OS grabbed the buffer and didn’t immediately pass it to the application.
Especially when the baud rate is 38400 or less.
This lag is a problem for our customer’s system.
Is there a way to improve it?

Best regards.

By the way, this problem does not occur with serial transfer over USB connection.
I think this is imx uart driver problem.
Please check this.

I was able to see an improvement by turning off the DMA.

Best regards.