Only when your computer actually has work to do. Otherwise your CPU is just a really expensive heater.
Modern computers are designed to idle at 0% then temporarily boost up when you have work to do. Then once the task is done, they can drop back to idle and cool down again.
> Timer Coalescing attempts to enforce some order on all this chaos. While on battery power, Mavericks will routinely scan all upcoming timers that apps have set and then apply a gentle nudge to line up any timers that will fire close to each other in time. This "coalescing" behavior means that the disk and CPU can awaken, perform timer-related tasks for multiple apps at once, and then return to sleep or idle for a longer period of time before the next round of timers fire.[0]
> Specify a tolerance for the accuracy of when your timers fire. The system will use this flexibility to shift the execution of timers by small amounts of time—within their tolerances—so that multiple timers can be executed at the same time. Using this approach dramatically increases the amount of time that the processor spends idling…[1]
[0] https://arstechnica.com/gadgets/2013/06/how-os-x-mavericks-w...
[1] https://developer.apple.com/library/archive/documentation/Pe...
Modern Macs also have two different kinds of cores, slow but energy-efficient e-cores and high-performance p-cores.
The p cores can be activated and deactivated very quickly, on the order of microseconds IIRC, which means the processor always "feels" fast while still conserving battery life.
There are a lot of such moments, but they are just short. When you're playing music, you download a bit of data from the network or the SSD/HDD by first issuing a request and then waiting (i.e. doing nothing) to get the short piece of data back. Then you decode it and upload a short bit of the sound to your sound card and then again you wait for new space to come up, before you send more data.
One of the older ways (in x86 side) to do this was to invoke the HLT instruction https://en.wikipedia.org/wiki/HLT_(x86_instruction) : you stop the processor, and then the processor wakes up when an interrupt wakes it up. An interrupt might come from the sound card, network card, keyboard, GPU, timer (e.g. 100 times a second to schedule an another process, if some process exists that is waiting for CPU), and during the time you wait for the interrupt to happen you just do nothing, thus saving energy.
I suspect things are more complicated in the world of multiple CPUs.
We’re not talking about what humans call “a moment”. For a (modern) computer, a millisecond is “a moment”, possibly even “a long moment”. It can run millions of instructions in such a time frame.
A modern CPU also has multiple cores not all of which may be needed, and will be supported by hardware that can do lots of tasks.
For example, sending out an audio signal isn’t typically done by the main CPU. It tells some hardware to send a buffer of data at some frequency, then prepares the next buffer, and can then sleep or do other stuff until it has to send the new buffer.
From human perception there will "always" be work on a "normal" system.
However for a CPU with multiple cores, each running at 2+ GHz, there is enough room for idling while seeming active.
My processor gets several whole nanoseconds to rest up, I am not a slave driver.
Not that I disagree, but when exactly in modern operating systems are there moments where there are zero instructions being executed? Surely there are always processes doing background things?