Prevent precise timers from being used when unnecessary

[glassez]

The implementation of QTimer::singleShot() uses Qt::PreciseTimer if interval is less than 2 seconds. This isn't mentioned in the docs.
Qt::PreciseTimer increases the system's timer resolution which negatively affects power consumption.

Closes #18350.
Supercedes #18475.

[sledgehammer999]

Maybe add something like this in the commit message?

The implementation of QTimer::singleShot() uses Qt::PreciseTimer if interval is less than 2 seconds. This isn't mentioned in the docs.
Qt::PreciseTimer increases the system's timer resolution which negatively affects power consumption.

Just to have enough context for the future.

[glassez]

Maybe add something like this in the commit message?

The implementation of QTimer::singleShot() uses Qt::PreciseTimer if interval is less than 2 seconds. This isn't mentioned in the docs.
Qt::PreciseTimer increases the system's timer resolution which negatively affects power consumption.

Just to have enough context for the future.

OK.
Added in OP.
Will add it in final commit message while merging.

[andry81]

Qt::PreciseTimer increases the system's timer resolution which negatively affects power consumption.

Can you elaborate the power consumption issue and give some links?

[glassez]

Can you elaborate the power consumption issue and give some links?

You can find something in the Issue mentioned in OP.
Also there is some explanation in Qt documentation: https://doc.qt.io/qt-6/qt.html#TimerType-enum.

[andry81]

Also there is some explanation in Qt documentation: doc.qt.io/qt-6/qt.html#TimerType-enum.

On UNIX (including Linux, macOS, and iOS), Qt will keep millisecond accuracy for Qt::PreciseTimer. For Qt::CoarseTimer, the interval will be adjusted up to 5% to align the timer with other timers that are expected to fire at or around the same time. The objective is to make most timers wake up at the same time, thereby reducing CPU wakeups and power consumption.

The meaning is to adjust wake up all types of timers at the same moment of time to reduce kernel scheduler switches. It does not much related particularly to Qt::PreciseTimer and power consumption.

[sledgehammer999]

The meaning is to adjust wake up all types of timers at the same moment of time to reduce kernel scheduler switches. It does not much related particularly to Qt::PreciseTimer and power consumption.

Qt::PreciseTimer forces the OS to use the smallest possible timer resolution. This results in more system wakeups than necessary. eg 1ms vs 14ms. Read the links in #18350 and the discussion thread in #18475