Re: Transport problem

   /etc/default/grub either needs to *not* mention preempt (default is 
full) or have preempt=full.  If you aren't experiencing any timing 
glitches then you should be ok.

Ted.

On 2/19/23 8:53 PM, chuck elliot wrote:
> I haven't noticed any problems but the current standard kernel in
> 
> Fedora 36 has:
> 
> CONFIG_PREEMPT_DYNAMIC=y
> 
> CONFIG_PREEMPT_VOLUNTARY=y
> 
> in /boot/config-$(uname -r)
> 
> does this need to be overridden in /etc/default/grub or in a kernel 
> rebuild ?
> 
> 
> 
> On 19/02/2023 5:19 pm, Ted Felix wrote:
>> Will, can you go through this first draft series of steps on the 
>> problematic box and let me know if it finds the issue?  Thanks.
>>
>> Boot into the problematic kernel.
>>
>> Confirm that it is a preemptible kernel.
>>
>>     $ grep -i config_preempt= /boot/config-$(uname -r)
>>     CONFIG_PREEMPT=y
>>
>> If you don't see "CONFIG_PREEMPT=y" then you need to install a 
>> preemptible kernel.
>>
>> Check the grub configuration to make sure nothing is specified on the 
>> kernel command line related to preemption.
>>
>>     $ grep -i preempt /etc/default/grub
>>
>> You should either see nothing or "preempt=full" along with possibly 
>> other options.  Anything else might mean trouble and requires a change 
>> to your grub config.
>>
>> Check for voluntary preemption.  (Not sure how this fits into 
>> everything, but it might cause problems and need some further 
>> investigation.)
>>
>>     $ grep -i preempt_voluntary /boot/config-$(uname -r)
>>     # CONFIG_PREEMPT_VOLUNTARY is not set
>>
>> Ted.
>>
>>
>> On 2/19/23 11:48 AM, Ted Felix wrote:
>>>    On second thought...  We've been here before.  From my Linux MIDI 
>>> Guide:
>>>
>>> --------
>>> Note: There are variations on PREEMPT that are less than ideal. 
>>> "DYNAMIC_PREEMPT" allows PREEMPT to be turned on and off in the 
>>> kernel command line options (preempt=full). You'll need to check your 
>>> GRUB configuration to make sure this is either set to "preempt=full" 
>>> or not set at all (the default is "full") in 
>>> "GRUB_CMDLINE_LINUX_DEFAULT=". You can check the setting after boot 
>>> with "sudo dmesg | grep preempt". There is also PREEMPT_VOLUNTARY 
>>> which is somewhere between "NONE" and "PREEMPT". You'll want to avoid 
>>> this as audio requires the best possible real-time performance.
>>> --------
>>>
>>>    I should probably make that a bit more prominent now that we are 
>>> running into it for real.  Like move it up to the "things you'll 
>>> need" section at the very top.
>>>
>>> Ted.
>>>
>>> On 2/19/23 8:52 AM, Ted Felix wrote:
>>>>    We rely completely on ALSA for timer stuff.  The key routine for 
>>>> setting the timer in RG is:
>>>>
>>>> AlsaDriver::setCurrentTimer()
>>>>
>>>>    Unless there is a bug in there (which there may very well be, the 
>>>> ALSA documentation is incomplete and in many cases incorrect), the 
>>>> problems tend to be due to bugs in ALSA or the kernel.  They usually 
>>>> get sorted over time by the ALSA folks. If they notice them.  This 
>>>> one seems like an interesting combination of requirements to 
>>>> reproduce and thus might fly under their radar.
>>>>
>>>>    I recommend building the latest kernel and seeing if that fixes 
>>>> the issue.  My three-year-old Debian/Ubuntu oriented notes are here 
>>>> if you need:
>>>>
>>>> http://www.tedfelix.com/linux/kernel-build.html
>>>>
>>>>    In general, it's really easy to do.
>>>>
>>>>    If it's still there, a bug report for the ALSA folks seems like 
>>>> the way to go.  They can help find the issue in ALSA, or even in 
>>>> Rosegarden if that's where the problem is.
>>>>
>>>> Ted.
>>>>
>>>> On 2/11/23 4:42 AM, Will Godfrey wrote:
>>>>> Recently I found Rosegarden was losing the timer source, and the 
>>>>> transport was
>>>>> freezing - sometimes for nearly a second after which it would send 
>>>>> a bunch of
>>>>> notes, then carry on as normal.
>>>>>
>>>>> It was some time before I realised it only happened on my Ryzen 5 
>>>>> machine (the
>>>>> one I use for music) and not on my office Intel one. I hadn't made 
>>>>> any changes
>>>>> to the system and got sidetracked into thinking maybe I'd somehow 
>>>>> managed to
>>>>> get infected with some malware. However I eventually remembered I'd 
>>>>> done a
>>>>> normal devuan update. The only significant change was the Linux 
>>>>> kernel V5.10 to
>>>>> V 6.1. Rolling that back cured the problem.
>>>>>
>>>>> Asking some questions on-line identified the problem.
>>>>>
>>>>> First off, I use the RT-Preemt kernel - the 'normal' one doesn't 
>>>>> have the issue
>>>>> at all.
>>>>>
>>>>> Secondly, the Ryzen has the AMD equivalent of hyper-threading, my 
>>>>> older Intel
>>>>> doesn't.
>>>>>
>>>>> Finally, since Linux V5.12 the scheduler has been modified to allow 
>>>>> dynamic
>>>>> preemption. Disabling this in the BIOS cures the problem, albeit 
>>>>> with a very
>>>>> small loss of performance.
>>>>>
>>>>> I wonder if there should be another look at how Rosegarden does 
>>>>> it's timing. I
>>>>> did try to set the timing source to the audio hardware. It seemed 
>>>>> to recognise
>>>>> it, but actually totally ignored it. Saving and reloading showed no 
>>>>> time source
>>>>> at all, yet still ran as if it was on System Timer.
>>>>>
>>>>
>>>>
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