[Opensim-dev] Sim and Phys Frames per Second (FPS) Issues

[Sean M]

Thanks Justin, Dahlia, Michael, and everyone. I now have a better
understanding of the way FPS is calculated and of the correction factor.

-Sean M.

On Monday, March 2, 2015, Justin Clark-Casey <jjustincc at googlemail.com>
wrote:

> I think this has already been said but just to summarize.
>
> * The 11 fps are the number of scene frames processed - opportunities
> where avatars may be notified about changes in the scene.
>
> * Each of these scene frames is associated with a physics process where 5
> physics frames are processed in each frame. Hence 11 * 5 = 55 fps.
>
> * Why this number?  Others may know better but my guess is that it's
> related to the frequency of updates expected by the viewer.  Teravus may
> well know more if he's still around.
>
> * Changing m_reportedFpsCorrectionFactor will do nothing except change the
> server FPS stat.
>
> * Changing MinFrameTime will change the number of scene frames.  From my
> work in the past, you would also need to adjust other parameters like
> physics frames to stop things going haywire (this was with ODE, Bullet
> might work differently).  I expect you also wouldn't gain much if anything
> in scene fidelity.
>
> On 02/03/15 18:23, Sean M wrote:
>
>> Greetings,
>>
>> We at the MOSES project have noticed Simulation and Physics frames per
>> second (FPS) have a few issues that we are trying
>> to resolve. The issues are producing suspicious performance statistics
>> for the analysis of the current version of
>> OpenSim that we are running.
>>
>> First, there is a correction factor (m_reportedFpsCorrectionFactor) that
>> the raw SimFPS is multiplied by. The comment in
>> the following line is a bit curious because it indicates that the FPS is
>> artificially inflated to "lie" about the actual
>> FPS being so low:
>>
>> OpenSim/Region/Framework/__Scenes/SimStatsReporter.cs: Line 317
>> // We're going to lie about the FPS because we've been lying since 2008.
>> The actual FPS is currently
>> // locked at a maximum of 11.  Maybe at some point this can change so
>> that we're not lying.
>> int reportedFPS = (int)(m_fps * m_reportedFpsCorrectionFactor);
>>
>> Also, lines 174 and 227 mention the use of this correction factor.
>>
>> Second, this multiplier also comes into play in the Scene where there is
>> a MinFrameTime, which seems to be the minimum
>> reported amount of time to process a frame:
>> OpenSim/Region/Framework/__Scenes/Scene.cs:Line 723
>>
>> Both of these variables, the correction factor and MinFrameTime, are
>> concerning from a statistics view point as they are
>> generating skewed and massaged numbers; therefore, I have a few questions:
>>
>> 1) Is it commonly known that Sim and Phy FPSs are inflated to maintain
>> the "lie"? And if so, will it be corrected to be
>> an accurate reporting of processed frames per second?
>>
>> 2) What exactly are the definitions for OpenSim's Simulation (Sim) FPS,
>> Physics (Phy) FPS and a frame (I have found
>> conflicting and vague definitions on the wiki)?
>>
>> 3) What are the known performance consequences of setting the
>> m_reportedFpsCorrectionFactor to 1 and MinFrameTime to 0?
>>
>> Thanks,
>> Sean M.
>>
>>
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>>
>>
>
> --
> Justin Clark-Casey (justincc)
> OSVW Consulting
> http://justincc.org
> http://twitter.com/justincc
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