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SubjectRe: 2.6 scheduler and "fast user switching"

Guy wrote:

>I typically log in as 'root' on the first console. I then invoke
>fluxbox as the GUI.
># XSESSION=fluxbox startx -- :0
>I then ctl-alt-F2 another console and login as 'user1'. I then
>invoke KDE as the GUI.
>$ XSESSION=kde-3.1.4 startx -- :1
>I may or may not ctl-alt-Fn and login as 'usern' and repeat the
>Several thoughts:
>1} I've seen Nick Piggin's suggestion of nicing X server to -10.
>At the moment, the only way I know to do this is something like
># XSESSION=fluxbox nice --adjustment=-10 startx -- :N

If you're not using my patches then nice causes scheduling latency
problems so don't do this even if you can. Con's scheduler work actually
makes interactivity good at the default priority.

>A} My default security is that only 'root' can perform nice with
>negative values. I am reluctant to play with security for such a
>crticial command.

Debian does this for you. I guess X runs as suid root anyway so
its not a big security problem.

>B} All child threads inherit the new nice value. So in the example
>just above, this means all applications started from the GUI
>desktop run at a nice value of -10. I believe enhancing the X
>server nice value this way defeats the purpose of nicing it to
>begin with. Obviously, despite my readings and attempts at
>research, I'm must be missing something here.

Debian manages to only renice the X server. If something like
this were required in a distro kernel I guess they would do it
for you nicely.

>2} I expect to travel down to Florida for Xmass to visit family.
>One of the things I had hoped to do was to set up my mother's
>computer as an X server and hang a thin client terminal {read:
>older PC} off of it. This would allowed my mother and brother to
>share a reasonably modern system at the same time.
>This is not me just being cheap. I'm interested in setting up
>diskless workstations aound a good central X server. I see such
>setups as appropriate for a number of situations. If the X server
>requires 'nicing' in a single user environment, what happens in
>an LTSP environment?

I think the server runs on the clients... or something ;)

>My base reference environment is 2.4.20. I still actively use it
>for everything I do as everything works as expected.
>Despite my enthusiasm for 2.6, I find it difficult to get
>everything to 'just work'. I still see problems in the area of
>nForce based mobos {stupid proprietary nVidia!}, broken BIOSes,
>and scheduler issues like the above.

Obviously make sure all your software is up to date with
Documentation/Changes, and remember we can't help with closed drivers.
If you still have problems please send in a report. Hope this helps


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