Re: [LAU] Ubuntu: changing realtime priority of irqs

On Sat, 2007-07-21 at 22:26 +1000, James Cameron wrote:
> On Sat, Jul 21, 2007 at 02:03:19PM +0200, Atte Andr? Jensen wrote:
> > Whereas on debian I would get:
> >
> > atte@email-addr-hidden:~$ ps aux | grep IRQ
> > root 18 0.2 0.0 0 0 ? S< 13:34 0:00 [IRQ 9]
>
> Which kernel version is this?

Homemade (with mingo rt-patch) 2.6.18-rt7

2.6.20-16-lowlatency

> On Debian, I get ksoftirqd as well, one
> per processor core. ksoftirqd is part of the 2.6 kernel series. I
> imagine you're still using a 2.4 kernel on your Debian system,

Nope...

> or the
> kernel is configured and built differently to mine.

Might be...

> It may be possible to rebuild the Ubuntu kernel you are using to match
> what you are used to, but I don't know if that will get you what you
> want.

I grabbed a vanilla 2.6.22.1 and applied the latest patch and quick
testing seems to suggest that the system is running at least at well as
under debian:

atte@email-addr-hidden:~$ uname -r
2.6.22.1-rt4

atte@email-addr-hidden:~$ ps aux | grep IRQ
root 36 0.0 0.0 0 0 ? S< 18:15 0:00 [IRQ-9]
root 268 0.0 0.0 0 0 ? S< 18:16 0:00 [IRQ-4]
root 292 0.0 0.0 0 0 ? S< 18:16 0:00
[IRQ-12]
root 293 0.0 0.0 0 0 ? S< 18:16 0:00 [IRQ-1]
root 1108 0.0 0.0 0 0 ? S< 18:16 0:00
[IRQ-14]
root 1139 0.0 0.0 0 0 ? S< 18:16 0:00
[IRQ-15]
root 1140 0.2 0.0 0 0 ? S< 18:16 0:02
[IRQ-11]
root 1936 0.0 0.0 0 0 ? S< 18:16 0:00 [IRQ-8]
root 2025 0.0 0.0 0 0 ? S< 18:16 0:00 [IRQ-7]
root 2103 0.3 0.0 0 0 ? S< 18:16 0:03
[IRQ-10]
root 3432 0.0 0.0 0 0 ? S< 18:16 0:00 [IRQ-3]
atte 4674 0.0 0.0 2888 772 pts/2 R+ 18:33 0:00 grep
IRQ

> I've never tried setting real-time priority on kernel threads
> like that, and I don't know if it would achieve anything. I trust it
> did for you?

Alot!

Bottom line: It seems it's still necessary to roll your own kernel to
get optimal realtime performance under ubuntu :-(

-- 
peace, love & harmony
Atte
http://atte.dk       | http://myspace.com/attejensen 
http://anagrammer.dk | http://atte.dk/compositions
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