How to increase the speed of UART

[jishnu M]

hi sir,

I make a software bridge between 2 uart of esp32 , here i am serially sending a file to uart0 and read that in uart2.
if i send a 1MB file (.txt file) it's taking around 9 minutes to receive file completely . i set baud rate as 921600. it's not changing the speed of file transfer if i increase or decrease the baud rate. why it's happens like this?,
What is the maximum speed of uart for data transfer in esp32?, How can i increase speed of data transfer?
i attached the program code