linux-kernel - Help low-jitter man.

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Message-ID: <50992F56.3080209@paradoxuncreated.com>
Date:	Tue, 06 Nov 2012 16:40:06 +0100
From:	Ove Karlsen <ove.karlsen@...adoxuncreated.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: Help low-jitter man.

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.

-- 
Fred være med deg / Peace Be with You,
Ove Karlsen
http://www.paradoxuncreated.com
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