Re: 2.6 scheduler and "fast user switching"

[Nick Piggin]

Guy wrote:

> Scenario:
>
> 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 
> process.
>
> 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

Nick


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