Re: [Lennart Poettering] Re: A few observations about systemd
On Mon, Jul 18, 2011 at 01:22:37PM -0700, Steve Langasek wrote:
> On Sun, Jul 17, 2011 at 06:51:17PM +0200, Lennart Poettering wrote:
> > In fact, a minimal systemd system will win in almost very aspect against
> > a remotely similarly powerful sysvinit system: you will need much fewer
> > processes to boot. That means much shorter boot times.
>
> This is, as far as I'm aware, an unproven assertion. While it's true that
> there is a cost to the additional processes used in init scripts, I have not
> seen any serious attempt at measuring how big this impact actually is -
> certainly not in terms that would be relevant to Debian, which uses dash as
> its /bin/sh and insserv by default (in squeeze and above).
>
> 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.
Mike
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