Re: [seq24-users] timing

[Elthariel <elt...@fr...>]

Please consider joining seq24-dev for talks about seq24 development :p

Thx

Ben Saylor wrote:
> Here's an update on my progress with improving seq24's timing on my 
> system, in case it someone might find it useful or have any additional 
> insights.
>
> The following page has some useful information on priorities and other 
> things relating to MIDI timing and audio:
> http://tapas.affenbande.org/?page_id=40
>
> I increased seq24's realtime priority above Jack's by setting Jack's 
> priority to 80 and changing line 1009 in perform.cpp from
> 	schp->sched_priority = 1;
> to
> 	schp->sched_priority = 85;
> and starting seq24 with the --priority flag (BTW, it would be nice 
> if --priority accepted an integer argument for the desired priority; 
> that's what I expected to happen at first but found that it was hard 
> coded).
>
> I increased the priority and frequency of the RTC (this is what seq24 
> uses for timing, right?):
> 	chrt -f -p 98 `pidof "IRQ 8"`
> 	echo 8192 > /proc/sys/dev/rtc/max-user-freq
>
> This seems to have improved MIDI timing.  However, when CPU load is 
> somewhat high (~50% in my test setup), switching desktops, launching 
> non-realtime applications, and especially moving windows can cause huge 
> timing glitches.  The sequence seems to pause and then catch up when I 
> stop dragging the window.  While this is happening, the audio continues 
> to play, and while enough window-dragging will cause audio dropouts, 
> the MIDI timing seems to go bad first, even though I've given seq24 and 
> RTC higher priorities than the audio apps.  I don't understand this, 
> and I don't understand why the timing should be affected so badly by 
> CPU activity caused by non-realtime processes, when all of the audio 
> and MIDI stuff has realtime priority.  Here's the output of top, sorted 
> by priority:
>
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>     9 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/0
> 2342 root      RT   0 10464  10m 1976 S  0.0  1.3   0:00.38 das_watchdog
>   236 root     -99  -5     0    0    0 S  0.0  0.0   0:00.00 IRQ 8
>  5815 me       -91   0 35736  34m 2584 S  0.0  4.6   0:00.00 jackd
>  5856 me       -86   5 39068  11m 9952 S  0.1  1.6   0:05.58 seq24
>  5816 me       -81   0 35736  34m 2584 S  0.8  4.6   0:12.37 jackd
>  5817 me       -80   0 29500  27m  16m S  0.0  3.7   0:04.44 qjackctl
>  5823 me       -80   5 51372  49m 7464 S 18.3  6.5   4:11.51 zynaddsubfx
>  5828 me       -80   5 61484  59m  26m S  1.4  7.8   0:22.76 hydrogen
>
> Then down below, there's another seq24 thread at priority -2.
>
> On Monday 21 August 2006 08:58, Ben Saylor wrote:
>   
>> Whoops, I meant to send this to the list.  I will check on the kernel
>> frequency when I get back to my computer.
>>
>> Rob Buse wrote:
>>     
>>> Ben-
>>>
>>> What frequency are you running the kernel at ?  I would suggest
>>> 1024Hz.
>>>
>>> Rob
>>>
>>>       
>>>> Hi,
>>>>
>>>> For some reason Seq24's timing isn't what it used to be on my
>>>> computer...  This is after a fresh install of Debian on a new hard
>>>> drive, but I installed exactly the same kernel I had before. 
>>>> Realtime priority is working fine with Jack.  I'm planning to do
>>>> some research on this issue, but does anyone have any pointers to
>>>> common causes of timing issues with ALSA MIDI or seq24 in
>>>> particular?
>>>>
>>>> Thanks,
>>>> Ben
>>>>         
>
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