How to set low latency in serial port open by QSerialPort - c++

Question

I have already developed an application and it performs serial communication with sensors.
For an unknown reason, my received data is slow with QT C++ Framework.
I have tested the sample code (https://www.pjrc.com/tmp/host_software/receive_test.c). I received data in the appropriate time with this sample code.
Here i found that low latency mode is set ASYNC_LOW_LATENCY.
I have read (https://doc.qt.io/qt-5/qserialport.html) but didn't get any idea about how to set low latency with QSerialPort
Q1: Please give a sample code in qt c++ with QSerialPort on how to set low latency.
Please don't suggest writing c code inside qt c++ this is not the right approach to solve this probleam.
QSerialPort *pUsbSerialPort;
pUsbSerialPort = new QSerialPort();
if(IS_VALID_OBJ(pUsbSerialPort))
{
pUsbSerialPort->setPortName(sSerialPort);
pUsbSerialPort->setBaudRate(BaudRate);
pUsbSerialPort->setDataBits(QSerialPort::Data8);
pUsbSerialPort->setParity(QSerialPort::NoParity);
pUsbSerialPort->setStopBits(QSerialPort::OneStop);
pUsbSerialPort->setFlowControl(QSerialPort::NoFlowControl);
if(pUsbSerialPort->open(QIODevice::ReadWrite))
{
connect(pUsbSerialPort, &QSerialPort::readyRead,this , &Laser::LaserReadyRead);
PRINT_INFO("Serial port successfully initialized" + sSerialPort);
bIsServeropen = true;
}
else
{
PRINT_INFO("Serial port initialization failed" + sSerialPort);
return;
}
}
else
{
PRINT_INFO(" Failed to assign memory to pUsbSerialPort" + sSerialPort);
return;
}

Answer 1

The descriptor is the Handle of the QSerialPort:
#include <sys/ioctl.h>
#include <linux/serial.h>
// ...
pUsbSerialPort->open(QIODevice::ReadOnly);
int fd = pUsbSerialPort->handle();
struct serial_struct kernel_serial_settings;
::ioctl(fd, TIOCGSERIAL, &kernel_serial_settings);
kernel_serial_settings.flags |= ASYNC_LOW_LATENCY;
::ioctl(fd, TIOCSSERIAL, &kernel_serial_settings);