Why does apt-get not use 100% of either cpu, disk, or network — or even close to it? Even on a slow system (Raspberry Pi 2+) I'm getting at most 30% CPU load. I'm just thinking that either it's being artificially throttled, or it should max out something while it's working … or it should be able to do its thing faster than it does.
Edit: I'm just measuring roughly via cpu/disk/net monitors in my panel, and the System Monitor app of Ubuntu MATE.
Please explain why I'm wrong. 🙂
Update: I understand that apt-get needs to fetch its updates (and may be limited by upstream/provider bandwidth). But once it's "unpacking" and so on, the CPU usage should at least go up (if not max out). On my fairly decent home workstation, which uses an SSD for its main drive, and a ramdisk for /tmp, this is not the case.
Or maybe I need to take a closer look.
Best Answer
Apps will only max out the CPU if the app is CPU-bound. An app is CPU-bound if it can quickly get all of its data and what it waits on is the processor to process the data.
apt-get, on the other hand, is IO-bound. That means it can process its data rather quickly, but loading the data (from disk or from the network) takes time, during which the processor can do either other stuff or sit idle if no other processes need it.Typically, all IO requests (disk, network) are slow, and whenever an application thread makes one, the kernel will remove it from the processor until the data gets loaded into the kernel (=these IO requests are called blocking requests).