On Mon 2007-10-29 15:48:20, Lennart Sorensen wrote:
> On Sun, Oct 28, 2007 at 06:07:07PM +0000, Pavel Machek wrote:
> > Hard stuff:
> >
> > * network character device -- similar to nbd, but for char devices.
> > either figure out how to forward ioctls(), or implement
> > usb-over-network, or...
> >
> > * openMosix -- they seem to have userspace solution, but not GPLed.
> >
> > * compression for ext4. Its about time someone did it right. Special
> > bonus if you can do it in a way that it does not slow down. If cpu
> > is free, compress, if it is busy, just write it straight to disk.
>
> So if I decide that the cpu is busy (because something is asking me to
> write the cpu is clearly doing something and hence busy), then I can
> skip compression and just write to disk. So by that definition ext4
> already does compression. What a simple project. :)
Tell it to your profesor ;-).
> Did you mean it ought to come back and do the compression later?
Not neccessarily but yes, that would be nice, too.
> Is it possible that for some data compressing it and writing will take
> less time than not compressing it and writing it to disk?
Yes. Typically for all zeros. It will be similar for
highly-compressible data (pictures, timetables, ....)
root@amd:/data/tmp# time ( cat /dev/zero | head -c 100000000 > delme; sync )
0.04user 0.48system 6.52 (0m6.521s) elapsed 7.97%CPU
root@amd:/data/tmp# time ( cat /dev/zero | head -c 100000000 > delme; sync )
0.05user 0.61system 6.33 (0m6.333s) elapsed 10.42%CPU
root@amd:/data/tmp# time ( cat /dev/zero | head -c 100000000 | gzip - > delme; sync )
1.57user 0.32system 1.74 (0m1.749s) elapsed 100.00%CPU
root@amd:/data/tmp# time ( cat /dev/zero | head -c 100000000 | gzip - > delme; sync )
1.61user 0.18system 1.65 (0m1.652s) elapsed 100.00%CPU
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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