Re: Help low-jitter man.

[Ove Karlsen]

On Tue, 06 Nov 2012 17:11:02 +0100, Ove Karlsen  
<ove.karlsen@xxxxxxxxxxxxxxxxxxxx> wrote:

> Den 06.11.2012 16:40, skrev Ove Karlsen:
> > Heya, it`s me again. I am getting my low-jitter E5 computer, soon, and I
> > have done all the tweaks I can think of with the kernel.
> >
> > I was wondering if anyone had anything to add, any good technical
> > opinion on reducing jitter (for workstation desktop/OpenGL).
> >
> > I have a kernel with "low latency desktop" enabled. And edited
> > Kconfig.hz to 90.
> > idle=poll and tick_skew=1 in boot options.
> > Compile a shaved local kernel by doing "make localmodconfig" from a full
> > distro kernel.
> > (Also turned of high_res_timers, to get 90hz)
> >
> > CFS granularity 1158500nS. (Current setting is a bit high)
> > Reniced X to -20, to prevent X being a bottleneck.
> > Remove 60hz limit in doom 3, to avoid timing jitter.
> > http://paradoxuncreated.com/tmp/AutoExec.cfg
> >
> > Some nvidia-specific stuff on my blog aswell :
> > http://paradoxuncreated.com/Blog/wordpress/?p=2268
> >
> > A lot of people think SLAB has lower jitter than SLUB etc, aswell, and
> > some tuning with regards to what kernel options execute the least code,
> > least background activity can be done. Opinions?
> >
> > I use SLUB currently, and have turned off mem-compaction.
> > And probably all kinds of debugging, counters and tracers.
> >
> > RCU boost to 99.
> >
> > I think I have collected most the relevant data for a low-jitter linux
> > config. but in case there is additional information, I would love to
> > hear it.
> >
> > Also ACPI on or off seems to be varying opions on. Some state ACPI
> > removes SMI`s? I don`t know what is true here, and knowing that some
> > recommend 10000hz timer for "low-jitter" (which is going the completely
> > wrong way) I would like to hear your opinion on this aswell.
> >
> > Also approaching a transparent OS, with realtime-threads is interesting.
> > Such as running maintask (optionally + depencies) as realtime.
> > Unfortunately it doesn`t seem to work so well with standard FIFO. Do you
> > think deadline could help this? Accurate 0.95ms of 1ms would be
> > interesting to try.
> >
> > Also if anyone knows a linux-distro with the same philosophy throughout
> > the OS, I would be interested to know about it.
>
> Also have anyone given any thoughts to vsynced HZ? And also even  
> possibly dividing subhz off that, or more hz counters if neccesary.

Ok, I think after this, simple renicing seems to reduce significant  
amounts of jitter. So then the question becomes, how far can you take  
renice.

Peace Be With you.
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