Alt+1

Is there a guide that explains all the readings found in ALT+1? I know a little about it, but would like to read up on all of it so I know exactly what I am looking at and what it means. What factors on it weigh the most.

I have attached the alt+1 reading from my home. Penrith has about 9 land owners and we all have right at 4096m land or more. None of us have a club or a store, its all basically residential. Penrith was routinely running at around 1800 fps before it was settled. Granted, only trees were there, but should this sim, less than a month into settlement look like this already? I have seen the fps down to 50 with just 11 people in the sim.

What is wrong with this picture and what can be done to help improve the status? I know my fps sucks, Im more concerned with the simulator stats. Thanks for any help in me understanding what this all means.

Run Tasks is taking up 75% of your CPU time. This is caused by various LSL functions. Check for excessive llListen, llSetTimerEvent, and llSensorRepeat.

To be more specific, it's taking up 75% of your sim's CPU time.

And now, the list:

Basic:

FPS - This is the number of Frames Per Second that are being rendered on your computer. It has nothing to do with the number or scripts in a sim, only the number of polygons and textures that must be drawn. In SL, your CPU is the most important piece of hardware where FPS are concerned.

Bandwidth - This is the amount of data being transferred to your computer.

Packet Loss - This is the amount of packets that are being dropped somewhere between Linden Lab and your computer. A cumulative packet loss indicator is inconveniently located in Help > About Second Life.

Ping Sim - Your ping is the amount of time it takes a signal to go from your computer to the another and back again. In this case, it refers to the the simulator server.

Ping User - This is the amount of time it takes a signal to reach the user server and back again. Ping Sim and Ping User are usually very close together, if not the same, because the computers are sitting right next to each other, and so data must travel the same route to get there. The only times they're likely to be radically different are when there's some kind of network issue going on with SL.

Unfortunately, I have to run here. Someone else explain the rest.

SimFPS means both a lot, and nothing at all. It's a strange formula involving 1/x of some kind. The higher it is, the faster your sim is running, BUT the difference in speed between 4000 and 2000 is the same as between 20 and 10. Also, anything over 100 in a sim full of avatars is wasted processing time (which means something close to maybe 600 in a mostly empty sim).

Thanks for the help. I still dont get it. My home feels laggy with those numbers I posted, but my neighboring sims feel fine and they have these stats... Sim East had 8 AV in it, 154 fps, 50.2% run tasks. Sim South had 4 AV in it, 2174 fps, and 56.8% run tasks. Both have dramatically different FPS, but they both feel fine, not laggy at all really. So its all still confusing to me.

Pete said, "Check for excessive llListen, llSetTimerEvent, and llSensorRepeat." What sort of objects use those functions? The scripts dont belong to me, I got rid of a lot of my scripts just to rule me out. I cant look at my neighbors stuff to see what the scripts are, what sort of items would use these scripts?

I appreciate the run down Catherine started, any more insight on how to mange the info on the Alt+1 feature would be great. Thanks again for taking the time to read and help out.

Well, in that case, Loki, it's likely a client-side issue. 8.8fps isn't exactly great. It's probably the number of textures and objects you're looking at that's doing it.

What kind of CPU, RAM and video card do you have?

Strange formula? I thought it was just 1/n where n is the time you spend computing a frame.
It should be a little over the sum of all those times you see in the alt 1 dialog.

Catherine touched on this, but I want to be a bit more explicit:

There are 2 systems involved when you are playing: The client (your computer) and the server (the "Simulation".

If EITHER one is laggy, you will notice. The Stats in the "Alt-1" screen display both: The numbers and big chart at the top are ONLY your local machine's stats - the ones under the "Simulation" heading are ONLY the server's stats.

If your home machine is running at slow FPS or doesn't have good connectivity (i.e. Bandwidth stuck down around 10 or less kbps), then the "Simulation" stats don't mean a thing - because your home machine can't keep up with the server (example: You press the button to move forward. By the time the Server gets the information that you've been moving, its been a 'long' period of time - so the server says "gee, this person should have moved a fair distance". It sends that back to your machine, and you see your avatar "skip" a bigger-than-expected distance. By the time your slow machine has processed the response from the server, drawn the screen, and updated again to tell the server not to move anymore, the server still thinks you've been moving all that time - so you continue to move for a little while after you release the key).

And the reverse is true: If your machine at home is running 60 FPS and the server is under a lot of load, your computer will be trying to update a lot more often than it can get new data from the server. Since the server is responsible for tracking where everything is in the world (including your avatar's movements), things will appear to "stutter" and not be responsive (because the server is playing "catch up" to your machine, your local machine thinks you've moved farther and the server thinks you've moved less. Since the server is always considered to be correct - for technical reasons I won't get into here - it "resets" your Avatar back to where it thinks it should be).

So you can see that "lag" and graphical glitches can come from a variety of sources.

Looking at the "Alt-1" display from top to bottom, here are some general tips:

FPS:

Movies run at about 24 - 27 FPS. Some people find 15 FPS comfortable, but for things to appear "smooth", you want 25 - 35 FPS at all times. The more "stuff" there is on the screen, the harder the video-card has to work, so you want to pay attention to these numbers when you're in an area with a lot of Shops or Avatars. This is because video cards draw almost everything in terms of little triangles - so everytime the screen is drawn, the video card has to solve mathematical equations to "build" what you "see" on the screen. I'll spare you all the technical details - but suffice it to say that its LOTS and LOTS of math to draw a screen full of objects. The more math the video card has to do, the longer it takes to complete the scene - and it can only draw the screen when ALL the math in one scene (or "screen-full" is done. The short version: The more (or further) you can see, or the more detail on the screen - the slower your video card will draw things. If you find your FPS below about 20, you really ought to go to the "Preferences" screen and turn off some of the Graphics detail. Here are some things to try, in a somewhat-prioritized list: Shorten your line of sight,Turn off Anisotropic Filtering, Turn off Bump-Mapping and/or Cloth effects, lower the Terrain detail, lower the Object detail level, lower the Avatar detail level, etc. "Fog" and "Gamma" options will do nothing for your FPS. Changing to a lower resolution will provide a slight improvement - especially on older hardware. But the line-of-sight or "view distance" will have the biggest impact.

Bandwidth:

If this is low, it might simply be that you're on a Dial-Up connection and have limited access. Objects and Music will download slowly - so turning down the graphics detail will help some when travelling to new areas. TECHNICALLY it will only help when your system is trying to load/rez new textures, prims, etc (i.e. when you're moving around in the world). If you sit in one spot without moving, adjusting your graphic detail won't really make a difference in the lag you experience due to bandwidth limits. If you are on dial-up and this appears to be low, you might call your DSL/Cable provider and ask if there is a problem. NOTE that SecondLife only uses as much bandwidth as it needs to - so again you will only notice a "High" amount of traffic when travelling to new areas that cause objects to be rezzed/loaded. Sitting in one place, even on broadband you'll see your Bandwidth sitting pretty low on the scale. If this goes "dead" or you experience a lot of packet loss, then something is wrong with the network connection between your machine and the server - possibly a problem on the internet; but also possibly a problem with your LAN (home network). I recently had problems with my router that were causing my bandwidth to get cut off every 5 minutes.

Whew, this is getting long so I'll take a break - but problems in the "Sim" part of the stats readout can only really be affected in two ways:

1) Get LL to put your sim on a better/faster server, or
2) Only allow a limited number of Avatars in your sim at any one time; and don't put up too many buildings / prims or scripts in the area.

Take care,

--Noel "HB" Wade
(Tread Whiplash)

Yeah, the problem with lag you're having is your FPS. Try turning off graphics options to speed things up, or buy a better CPU and/or graphics card. (The CPU is better for improving performance of local lighting, the GFX card is for everything else.)

My fps is low, I know. But, I would rather see things better than look at a bland landscape. I can get by without lagging the majority of the time. I have tweaked my fps many times and know what I need to do to improve my end. I can sacrifice my fps in order to see things better. However, I do appreciate the insight in regard to my actual settings. My settings work fine most places, if I get to where I cant play, I will make some changes.

My real concern is understanding how simulators themselves work. What do all the things on the alt+1 graph mean and how do they effect the sim performance. How can some sims that have worse numbers actually perform better than others? Is it just a mystery or is there a real way to analyse the stats and understand it all?

Under the "Simulator" section:

Time dilation: This is one measure of physics lag. If it's less than 1.0, it means everything in the sim is going to move slowly, since the server needs more time to compute physics interactions. The most common causes for this to be low are very large numbers of physics objects, or collisions between oddly-shaped prims.

Agent updates/sec: This is how many times a second the server can send updates on the state of the world to you.

Physics FPS: This is how many times per second the server is updating the state of physics-based objects. See "Time dilation" for what's happening if this is below 45.

Sim FPS: This is how many times per second the server can do a full update of the non-physics server state. It's an overall measure of how busy the server is; higher numbers are better. If it's below 100, you'll start to feel lag.

Main agents: This is how many users are in the sim.
Child agents: This is how many users can see the sim.

Active objects: This is how many objects in the sim are physics-based or have running scripts.
Active scripts: This is how many scripts there are in the sim.

Sim CPU: Theoretically, this is an overall indication of how busy the server is. In practice, it really is an indication of what sort of system the server is running on.
1.00: Non-hyperthreaded CPU, either an Opteron (very good) or an early Pentium IV (not so good)
0.50: Hyperthreaded Pentium IV (good).
0.25: Sharing a server with four other sims. Only seen in the void sims.