Parallel Booting

[Colin Walters]

On Fri, 2007-07-06 at 17:31 -0400, Alan Cox wrote:
> On Fri, Jul 06, 2007 at 04:55:47PM -0400, Colin Walters wrote:
> > Possibly, but I think the biggest speedup by far is the disk
> > caching/reorganization that both Windows and OS X do: 
> > http://www.kernelthread.com/mac/apme/optimizations/
> > 
> > At this rate though, we might all be using solid state drives before the
> > kernel developers stop pointing at userspace as the problem and
> > implement it for Linux.
> 
> We already lay stuff out very carefully and precache. 

What precaching?

Ok, I just googled and found a really good thread:
http://kerneltrap.org/node/2157

It's unclear to me though how much of this is actually running now.

The MacOS X page I linked to claimed that when they disabled the
filesystem boot cache, it almost doubled boot time (in other words, the
cache halved boot time).  That says to me that either

1) Our precaching isn't as good as their implementation
2) MacOS X is fundamentally different

I think it's more likely to be 1.  I could be wrong though.

> Years ago I sent the gnome team a library that could load and
> linearlly
> map the entire theme in about 3 syscalls coming out nicely on disk.
> They
> never used it.

I believe the icon cache is currently
mmap'd: /usr/share/icons/hicolor/icon-theme.cache

Whether it's your actual code or not I don't know.

> Unfortunately most
> of the mess *is* userspace 

Right.  That doesn't change the fact that some kernel work seems very
likely to speed things up quite a bit.

> and some of the userspace authors are in
> complete denial. Just profile the number of file opens of different files
> done in a gnome startup and when you've finished laughing you can weep.

Work continues on improving userspace:
http://primates.ximian.com/%7Efederico/news-2007-06.html#26