Profiling before you optimize [LWN.net]

Profiling before you optimize

Posted Jul 21, 2006 8:41 UTC (Fri) by Thalience (subscriber, #4217)
In reply to: OLS: On how user space sucks by ekj
Parent article: OLS: On how user space sucks

Do you have profiles to support the idea that hardware autodetection is a big component of the startup time? It could be, but watch out for optimizing blind.

I'd take reliable hardware auto-dectection over a static configuration at any reasonable cost, just as a matter of personal preference.

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Profiling before you optimize

Posted Jul 27, 2006 7:54 UTC (Thu) by ekj (guest, #1524) [Link]

Not scientifically valid profiles, no.

But bootup-time (measured from GRUB loads the kernel until the last startup-script finishes) improved from 1:48 to 1:32 simply by disabling kudzu (which does detection of new hardware).

Uninstalling packages that where auto-installed without question, and that support hardware I don't have shaved another 10 seconds off that to aproximately 1:23.

1:23 and 1:48 ain't that hugely different, but it *does* mean a 30% increase in bootup-time for trying to detect hardware I don't have on every bootup.

Some hardware is regularily plugged in an out. It's reasonable (and good) to try to detect such. But that should happen on the fly, and not as part of a bootup-script. Afterall, the user may very well plug in a usb-stick or whatever *after* logging in.

Other hardware (like for example a pcmcia-slot) is rather unlikely to suddenly appear. I'm guessing that 99.9% of the computers that don't have it when the distro is installed, will *never* have it.

Profiling before you optimize

Posted Jul 27, 2006 17:26 UTC (Thu) by Thalience (subscriber, #4217) [Link]

Ok. Those are reasonable numbers to work with. Thanks for making the effort!

I still think, however, that ditching auto-detection would be to throw the baby out with the bathwater. By focusing more attention on hot-plug style auto-detection, we can have both fast startup and reliable, effortless hardware support.

As an aside, I've always thought that Kudzu was a very appropriate name for that particular peice of software. :)