Test results of Qsynth running on Xubuntu 11.10, compared with Ubuntu 11.04

[Gustin Johnson]

Have you looked at the rtirq stuff to improve the performance of 3.x
kernels?

On Sat, Nov 26, 2011 at 7:18 PM, Aere Greenway <Aere at dvorak-keyboards.com>wrote:

> **
> Ubuntu Studio Users:
>
> I think your plan to move Ubuntu Studio to Xubuntu is a good one.  It
> seems to have the lowest overhead of any of the Ubuntu versions.
>
> But it seems there are problems with the kernel itself, which even the
> lower overhead of Xubuntu cannot solve.
>
> I have been working with the Fluidsynth developers to address another
> problem, and in doing so, discovered the performance problem the testing
> below attempts to quantify.
>
>
> All:
>
> Your suggestion of cutting the sample rate did not seem to have any affect
> that was visible to me.
>
> It may be that I would need to run without Jack, but I need Jack because I
> use audio files.
>
> In the past, I have run without Jack, and the performance of Qsynth was
> better, but not much better.  I could test this further, but it is a moot
> point, since I need to be able to use audio files in my sequences.
>
> I performed some benchmark testing on the problems I have been reporting.
>
> I did all of the following on a 933 megahertz unit-processor (one CPU)
> machine, which has been my minimum system in my test-bed.
>
> I tried it on Ubuntu 11.04, and on Xubuntu 11.10.
>
> My methodology was to reduce the Qsynth polyphony parameter to the point
> where my test sequence (MIDI) file yielded no underruns.  I did a binary
> search for the polyphony value that worked.  I did not use Reverb, or
> Chorus (the check-boxes were clear) in any of the tests.
>
> With polyphony values above 16, changes of  1 (up or down) made an
> observable difference.
>
> I also noted (while the piece was playing) the Digital Signal Processing
> load (shown in the Qjackctl window as Real Time Percentage (RT %).
>
> When I got down to the minimum Qsynth polyphony value of 16, I started
> muting tracks, to where the maximum # of single-note-playing-at-a-time
> tracks played with no under-runs.
>
> *UBUNTU 11.04*
>
>
> Polyphony parameter value without under-runs:    *26*
>
> DSP Load while playing:     Usually in 20% range, sometimes in 30% range,
> max 38.9%
>
>
> *XUBUNTU 11.10*
>
>  Polyphony paramater value without under-runs:    *3* (16, with only 3
> tracks playing!)
>
> DSP Load while playing:    In the 50% range, often getting up into the 60%
> range.
>
> *Note: It will not play a single-track piano part without generating
> under-runs.
>
>  From past experience, I observed that UBUNTU 11.10 has a poorer
> performance than XUBUNTU 11.10.  Also, the Unity desktop appears to have
> DSP Load values 20% higher than the cripple-ware Ubuntu Classic desktop on
> the same machine.
>
> As you can see, the performance of the two systems is radically different
> - an order of magnitude.  It is not just a minor difference.
>
> The performance hit seems to be associated with the new kernel - not so
> much the desktop.  Though Kubuntu had the poorest performance of the three
> I tried.
>
> A 2.5 gigahertz unit-processor system (using the Ubuntu Classic desktop)
> will run the test piece without under-runs.
>
> I have a 1.5 gigahertz machine which I have not yet tried, but based on
> the above, it will perform poorly, or perhaps marginally.
>
> On 11.04, all of these machines would perform the test piece on Qsynth
> without under-runs (though on the 933 megahertz machine, the Qsynth
> polyphony had to be set down to 26).
>
> I will do further testing with my 1.5 gigahertz machine, since this is one
> of the target machines I originally planned to use.
>
>   --
>
> Sincerely,
> Aere
>
>
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