Re: Transport problem

   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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