Innodb_read_io_threads is the variable for configuring the number of InnoDB threads handling reads requests. The innodb_write_io_threads
variable is the other half of the I/O threads equation and is for configuring the InnoDB threads handling write requests. These two variables work across MySQL, Percona, and MariaDB.
Each thread is capable of having 256 I/O requests in a pending state. For example, by setting innodb_read_io_threads to 2, the system will handle 512 concurrent asynchronous read I/O requests. InnoDB will attempt to balance the pending I/O requests across all available threads.
InnoDB I/O asynchronous subsystem is controlled by the innodb_use_native_aio variable, which is enabled by default.