Kernel build performance [LWN.net]

Kernel build performance

Posted Nov 25, 2009 12:08 UTC (Wed) by mingo (subscriber, #31122)
In reply to: Kernel build performance by tialaramex
Parent article: The 2009 Linux and free software timeline - Q1

It's not /pure/ chance, it's partly because people adjust their behaviour in order for things to come out as expected. When you're a bit late you run for the train, and when you're early you stop to look at the clouds in the sky.

Yeah it's not pure chance, but note that none of the factors i cited are really any 'macro behavioral' items. People don't speed up or slow down the kernel build via a single act - their micro-changes have _way_ too little effect on it as a whole. It literally needs a thousand changes for anything like this to show up in any wall-clock measurement.

(Sometimes there's feedback in terms of 'hey you made the kernel build slower' - but these aren't efforts that stabilize it - these just affect the basic parameters and the combination (end result) is random.)

But i'll certainly agree that people wouldnt accept 30+ minutes kernel build times - nor would they stop from bringing its speed from 10 seconds to 20 secods (halving build performance, without anyone really complaining). So there's a certain psychology driven behavior that keeps it somewhat within a given "band" of performance - but the fact that kernel build times are pretty stable over the past decade is pure chance i think.

But i think i digress :-)

(Log in to post comments)

Kernel build performance

Posted Nov 25, 2009 14:13 UTC (Wed) by nix (subscriber, #2304) [Link]

people wouldnt accept 30+ minutes kernel build times

Your enormous hardware budget is showing :) until I upgraded this year I had never owned a machine nor even seen a machine which could build a kernel in less time than that. Multi-hour-long build times are not unknown, though admittedly you need to use 1999-vintage hardware for that, which is pushing obsoleteness even among those of us with near-nil hardware budgets.

Kernel build performance

Posted Nov 25, 2009 15:41 UTC (Wed) by mingo (subscriber, #31122) [Link]

Your enormous hardware budget is showing :)

You are making assumptions :-)

I regularly build the kernel on stock laptops and desktops (which are typically 1-2-3 generations older than state-of-the-art) and the build times are well below 30 minutes. (usually within 10 minutes.)

The oldest system on which i still build the kernel is a 833 MHz P3 laptop with 512 MB of RAM, there a typical kernel takes 45 minutes to build. (But that's ~5 generations old and kernel developers/testers rarely use such old systems.)

I never build distro kernels though - i always use (and used) .config's tailored to the specific hardware. You can certainly waste a lot of time by building generic kernels.