[LAU] RT kernel

[Ralf Mardorf]

On Fri, 4 Nov 2016 11:44:47 +0000, Yassin Philip wrote: 
>By the way, does the rtirq-init IRQ balancing script
>work with this kind of kernel? It seems to launch OK, but given its
>description "startup script for realtime-preempt enabled kernels" does
>it do anything good on a lowlatency system?
>
>Does anybody here use lowlatency kernels, and do they come with
>special usage tips and recommendations?

The lowlatency kernel is a 'normal' kernel, just with 'threadirqs'
enabled. If you use the boot option 'threadirqs', then a 'normal'
kernel is a 'loalatency' kernel, too. The Ubuntu maintainers might
change some options that differ between a so called 'lowlatency' and
'general' kernel, e.g. CONFIG_HZ=1000 instead of CONFIG_HZ=250, or
CONFIG_PREEMPT=y instead of CONFIG_PREEMPT_VOLUNTARY=y. However, both
are vanilla kernels, perhaps with Ubuntu patches, that wouldn't make any
sense at all.

The PREEMPT options make a difference, but HZ=1000 unlikely makes a
difference at all. MIDI software timer anyway should be HR timer and I
don't know if it makes a difference for audio.

FWIW NO_HZ settings are the same for 'general' and 'lowlatency' kernels.

Yes, rtirq does work for rt patched kernels, for 'normal' kernels, such
as the lowlatency kernel, if 'threadirqs' is used. IOW for 'lowlatency'
by default and for 'general' if you add the boot option 'threadirqs' to
grub.cfg or somewhere in the config files for the config file. I edit
grub.cfg directly.

Regards,
Ralf