Ask HN: Why does running a few instances of DIR /s in Command prompt load CPU heavily?

https://news.ycombinator.com/item?id=465508

by fzkl • 17 years ago

2 3 17 years ago

news.ycombinator.com

Opening 3-5 windows command prompt and running DIR /S to list all subdirectories increases CPU load to 80%. I have seen this type of significant load on the CPU in different platforms. Any idea why a simple task like directory listing consumes so much CPU?

jacquesm• 17 years ago

That's because you are the only user on the system and you're asking the filesystem to tell you everything it knows about all your files.

Strictly speaking it is an io-bound operation, but with the number of files on your machine and some aggressive caching it will quickly turn into a memory-to-display translation (involving lots of font rendering and scrolling) and that is cpu-bound, not io-bound.

Look at it this way, the 'idle' process also consumes lots of cpu power, but it does absolutely nothing. When you're alone on a machine you have the power to max it out with anything cpu bound, no matter how simple. A loop that counts from 0 to 1.000.000.000 (assuming it's not optimized out) will consume 100% cpu time unless you tell your system explicitly otherwise.

The only way to not max out the cpu is to deliberately slow the process down by installing small sleep periods in between operations, but you really want your 'dir /s' to run as fast as it can.

gaius• 17 years ago

Indeed - as an experiment, try doing the same with all your CMD windows minimized.

fzkl• 17 years ago

Thanks

Ask HN: Why does running a few instances of DIR /s in Command prompt load CPU heavily?

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