On Mon, Jul 18, 2011 at 11:14:39PM +0200, Mike Hommey wrote: > > I'm sure that systemd does much better than a traditional sysvinit boot with > > /bin/bash and no dependency-based booting. But then, so does Debian's > > current boot system, and so does upstart; and neither of the latter two > > involve grandiose claims of a "shell-free boot". Trying to take the shell > > completely out of the boot means a definite tradeoff here between boot speed > > and configurability/maintainability, and in the absence of hard numbers, I > > suspect this is a false optimization and not a trade-off that we actually > > want to make in a general distribution. Which then calls into question the > > use of such claims as a justification for a switch to systemd at all... > I'd expect some important differences between shell script based init > and systemd-type init by the simple fact that there are (or at least > should be, I don't know how systemd actually works) less files to read. > Less files to read == less disk seeks. Disks seeks hurt startup performance. Yes, I've read your blog entries on the subject. :-) That's true, but I think the reduction in the number of files being accessed, for systemd vs. sysvinit or upstart, is rather small; aside from some things in /etc/rcS.d, most init scripts would have approximately a 1:1 correlation with upstart jobs or systemd config files, and if you've read the shell off disk once it's in cache and there's not likely to be any more seeking. So I do expect that most of the shell penalty will be CPU rather than disk in the context of boot. -- Steve Langasek Give me a lever long enough and a Free OS Debian Developer to set it on, and I can move the world. Ubuntu Developer http://www.debian.org/ slangasek@ubuntu.com vorlon@debian.org
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