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JoyofRLC Acker

Understanding Lag - Blake Sea Arabian (yes, I know!)

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This is a multi-part question; both conceptual and specific)

We have had an issue in Blake Sea Arabian since late last week (and until this morning) with Time Dilation fluctuating between 0.1 and 0.97 or so, frequently below 0.9 for sustained periods.   No obvious causes; usage hasn't changed etc - TD is usually in the 0.95+ range.   Restarts seem to have fixed it this morning - so far!!

The first question is - do any Lindens reading this have access to any stats or info that would indicate the cause?   Even in general, if not specific.

The conceptual questions start with Spare Time.   Im not clear if that is Total Frame Time - Net - Physics - Scripts, in which case my question is how is total Frame Time calculated?  Or if Total Frame Time is Net + Physics + Scripts + Spare, in which case, how is Spare time calculated.

Am I correct that Time Dilation is something line (22.22 / TotalFrameTime)?

And am I right that Spare time needs to be over say 20 to avoid discernible lag?   The real question is why?   Its as if Spare time really isnt Spare, but in fact something else is happening in that time.

If that is the case, why are there no stats on the hidden work, so that Spare time is truly spare, and values > some small margin indicate a healthy sim.

Hoping someone can help me!

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You're looking at things slightly backwards. The important numbers to look at are "Sim FPS" and "Physics FPS." In a perfectly running region they should always be at 45. In reality, they often are slightly slower for moments when a new load happens like a new avatar entering the region. "Time dialation" is how close the region is coming to the optimum 45 frames per second. Brief fluctuations aren't usually a problem - it's when the framerate goes below 45 and stays there that you notice perceptible lag.

The way the simulation is written the framerate will never go more than 45 frames per second. (This is the actual number of times the simulator tracks objects, avatars, etc. and has nothing to do with your visual frame rate.) "Spare time" is injected into the equation when the processes run each frame would take a total of less than 1/45 of a second to run. This helps maintain a consistent simulation framerate.

Scripts used to be a major cause of laggy regions but some years ago the simulation was re-written so that scripts could only use a certain amount time per frame and any scripts that couldn't run in that time would be skipped and run in the next frame. This is why there's a "Scripts Run" percentage - that's the percentage of possible scripts that get to run in each frame. When that number starts dropping the scripts themselves will run more slowly and erratically but the overall region should keep performing at the optimum framerate.

 

 

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Hmmm ... I was looking at the FPS so cant quote values but Id guess they were low.

So the Net, Physics and Script ms times dont matter?   

We're sailors (scripted vehicles) so aside from all that, a low script % would be a problem even if everything else was Ok (boat would be non-responsive).

Im still not clear what is going on during the "Spare Time" and why it needs to be so large.

Also ... how do Homesteads factor in this?  Does each sim on the server get its own 22.2 ms frame time?  Can one sim impact the others?
(Arabian is a Homestead).

 

 

Edited by JoyofRLC Acker
forgot to add something

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17 hours ago, JoyofRLC Acker said:

The conceptual questions start with

First of all, there are different TYPES of lag...

There is server side lag, net lag, and client lag,  and these have subsets, for example client side lag can be gpu based lag, where your pc has problems rendering the scene, or simply that your pc has a slow cpu, or that theres too many other tasks running on your pc. Same goes for net lag, I'm often amused by people claiming sl is lagging for them, and when you ask, they are playing skyrim in another window, and have netflix streaming a movie or 3 in HD...

Server side lag... Yeah, well, first you need data, Crt;l-Shift-1 gets you a handy and confusing popup.

Sim FPS & Physics FPS and dilation are often claimed as THE important numbers, reality is by the time these numbers show any significant drop off, its already a sim in deep deep trouble. Generally, you can ignore these 3 numbers, they are Final Doom warnings.

More useful are the numbers at the bottom of the readout.

Simulators try to keep the frame time at around 22-23 milliseconds.

The frame time is the total of script time, agent time, physics time etc., and there is a priority to these.

The simulator WILL prioritise physics time over script time, so if the physics time goes up, because there are physical prims on the sim (vehicles, dies, griefer cubes, amusing cows from cow launcher guns, whatever) then it will automatically reduce the script time to keep frame time at around 22-23 ms. This can cause the % of scripts run (higher up the display) to drop dramatically, menus start failing, scripted controls on vehicles become unmanageable, etc.

Bluntly, too many boats on a sea sim, and the steering on all of them goes to hell in a handcart. Everyone complains about the 'lag' and some clueless smartass says smugly "but the Sim/Phys FPS are both 44.9, everything is fine..."

This is why for example 'persistant temp re-rezzers' are banned on many private estates, because their habit of rerezzing stuff every 30 seconds, causes major dips in a sims performance, like a heart beat, which can even affect the SIM/Phys fps figures, with pulsed drops of 60%, its the physics time. This is also why griefers attack with self replicating BOUNCY physical prims, fastest way to kill a sims performance. Attack the physics time.

Lag meters that JUST show Sim FPS/Phys FPS/Dilation are basically, useless...




 

Edited by Klytyna

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