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Re: Parallel Booting



On 7/6/07, Alan Cox <alan redhat com> 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. Unfortunately most
of the mess *is* userspace 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.

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.

That isn't to say the kernel is perfect and there is a ton of optimising
work still going on, different scheduling algorithms and the like but
most of the slowness is from user space - some from tools, some from
combinations of tools and kernel (eg linker and paging patterns) and a lot
of it from sheer stupid clueless design of applications and especially
of GUI libraries.


Speaking from my many days as a performance analyst, Pfeifer's first
rule of performance says "The only good I/O is one you don't do".

I'll second Alan here. The OS can mitigate the effects of I/O but
userspace has the onus to be reasonable.

darrell


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