[LAU] Ubuntu: changing realtime priority of irqs

[Atte André Jensen]

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 at ajstrup:~$ 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 at ajstrup:~$ uname -r
2.6.22.1-rt4

atte at ajstrup:~$ 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

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