[PlanetCCRMA] Akmod for the realtime kernel

[Fernando Lopez-Lezcano]

On 1/9/22 11:21 AM, Fernando Lopez-Lezcano wrote:
> On 1/9/22 4:39 AM, Yoann LE BARS wrote:
>>
>> Hello, everybody out there!
>>
>> On 2022/01/09 at 12:44 am, Nils Tonnätt wrote:
>>> If you can wait until 5.16 is released on Fedora, you should be able 
>>> to just pass preempt=full as a boot parameter.
>>> Dynamic preemption is in the kernel since some kernel versions, but 
>>> it wasn't enabled in Fedora, because you
>>> couldn't set it up in a way that satisfied the Fedora kernel 
>>> maintainers. That changed in 5.16.
>>> So I hope they remember to turn it on.
>>
>>      Thank you for this information, this is good news. I guess I can 
>> wait until 5.16.
> 
> I think you do not need to wait till 5.16 if you want to try this, 
> current Fedora kernels do have this option but it is turned off by 
> default as Nils pointed out (ie: without configuration the kernel boots 
> into PREEMPT_VOLUNTARY instead of PREEMPT_FULL). I think the option was 
> introduced in 5.12 (5.13 certainly has it).

Nils pointed out to me off-list that there are two options:

CONFIG_HAVE_PREEMPT_DYNAMIC
and
CONFIG_PREEMPT_DYNAMIC

The second one (much more recent) I don't have, and I have not been 
using, obviously.

I had thought I saw differences when booting with that option but maybe 
I was fooling myself, would not be the first time (ie: audio stuff that 
was having xruns did not after the change, maybe it was something else).

I have to dig more on this.... more later today...
-- Fernando


> It is very good news if this is going to be ON by default!
> 
> Just add "preempt=full" to the boot options line in /etc/default/grub 
> and redo the grub configuration file. Do a "dmesg|grep preempt" to check 
> that it is active after rebooting.
> 
> I am using preempt=full myself for audio work and it is enough for my 
> purposes (I used to run the rt patched kernel[*] because the stock 
> Fedora kernel was pretty bad in that respect).
> 
> Best,
> -- Fernando
> 
> [*] actually these days I cannot use the rt patched kernel as it is not 
> good for running the custom motu sound driver described in the 
> linuxmusicians thread on the motu - too many interrupts and context 
> switches make the video unusable....
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