Processor occupancy

[ADVUser]

Hi everyone,

I have a problem with my processor occupancy.
I am working on Windows 7, my processor is an Intel core i5 4460 (4 cores 4 threads).
I created a cpp qt program with a main thread (GUI), and two others threads (one for an Ethernet communication and the other to read a file).
I had a problem on this program (now solved) which occupied a lot the processor. But the maximal processor occupancy was 50%. I don't know why ...
Do you have an idea ?

Thank you !

[A Former User]

Hi! Did I get this right, you're basically complaining that your bug only fried a single core? :-D

[DRoscoe]

I'm not sure I understand the problem, but you could be looking at a feature of the processor hardware. With i5 and i7 processors, it can actually split a single thread across more than one processor core. In theory this prevents poor performance from a processor-hungry process. Historically this was not done because the cache thrashing would negate any benefit. However, i5 and i7 has a cache for each core in addition to the L3 cache shared by all. I have seen this same behavior in my application. It employs a genetic algorithm which gobbles up 100% of the processor for 10+ seconds at a time. However, when I look at the performance tab of Task Manager, I see its actually splitting it across two cores at 50% each.

[ADVUser]

I wanted to know why I can't go above 50%, while I have got 3 threads ...

[JohanSolo]

@ADVUser said in Processor occupancy:

I wanted to know why I can't go above 50%, while I have got 3 threads ...

Maybe your processing has some blocking command, which result in an average usage of 2 threads running at full speed. Fortunately, N threads in a program does not necessarily in N / n cores used at 100%.

[A Former User]

Just as a test, the following should work:

heater.h

#ifndef HEATER_H
#define HEATER_H

#include <QObject>

class Heater : public QObject
{
    Q_OBJECT
public:
    explicit Heater(QObject *parent = 0);
public slots:
    void process();
};

#endif // HEATER_H

heater.cpp

#include "heater.h"

Heater::Heater(QObject *parent)
    : QObject(parent)
{
}

void Heater::process()
{
    auto a = 0;
    auto b = 0;
    while (true) {
        a = ++b * ++a;
    }
}

main.cpp

#include <QCoreApplication>
#include <QThread>

#include "heater.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    const auto thread_count = 8;
    for (auto i=0; i<thread_count; ++i) {
        QThread* thread = new QThread;
        Heater* heater = new Heater();
        heater->moveToThread(thread);
        QObject::connect(thread, &QThread::started, heater, &Heater::process);
        thread->start();
    }

    return a.exec();
}

[ADVUser]

Thank you for this code, it explains such things...
It is interresting to modulate the thread count number
Bye !