Sunday, August 24, 2008

Some Notes on ARC

I'm hearing a lot of talk about ARC in regards to Hair Fair, and it's a huge peeve of mine. ARC is not reliable. There are serious problems with the criteria it uses; it gives a ballpark figure only.

What's wrong with it? Well, you can read how it works here, but I see at least three problems with it:

1. It ignores polygon count. For those of you that don't know, more polygons means more for your computer to render, which means more lag. All prim attachments get 10 points, regardless of how many polygons they have. A box (very few polygons) generates the same ARC number as a sculptie or torus (lots and lots of polygons), despite the fact that the actual lag created by these prims is quite different.

2. It ignores texture size. The bigger a texture is, the more lag it creates, and big textures are quite a bit bigger than small ones. (A 1024 x 1024 texture, for instance, is as large as 16 256 x 256 ones.) Nonetheless, ARC gives 5 points for texture, regardless of size. A 1024 x 1024 image is significantly laggier than a 32 x 32 one, but both will rack up the same ARC number.

3. The accounting for size is a bit too crude. Attachments get one point per meter of size, per axis. While bigger prims do lead to more lag, I wish the scale were a bit more refined. A hundred prim hair and a hundred prim necklace are unlikely to generate the same amount of lag: those necklace prims are probably so teeny that they're quickly culled (i.e., not rendered at all) as you zoom out. I know that the jewelry I make tends to lag me less than the hair I make, even though it usually has more prims.

ARC is not entirely useless. Someone with a very low number is unlikely to be generating a lot of lag (above and beyond what all avatars generate, that is), and vice versa for someone with a very high number. But the numbers are very, very rough, to the point of -- in my opinion -- being misleading.

So stop quoting them, 'kay? It's making me twitch.

Oh, and one more note on Hair Fair: people and their attachments are, at this point, not entirely to blame for the lag. Oh, they're lagging you, but Hair Fair would be painfully slow even if they were all bald and naked. The sims themselves are slow right now, as they struggle to handle all the avatars. When I went yesterday, my frame rates were fine, and I still could barely move. That wasn't my computer having trouble rendering Blingy Lady #55 and her hair, it was the sim server faltering.

13 Comments:

Blogger Ana Lutetia said...

Thank you, Miriel, for the enlightenment. Gwyneth Llewelyn wrote a post about the lag myths some time ago when I made the same mistake of blaming other people because of my lag.

August 24, 2008 5:27 PM  
Blogger Allegory Malaprop said...

Do the sitting on box thing! It's awesome. Find one of the red boxes Sasy has left around (build is on in 3 of the sims, but Pink is partly or entirely off, so your own box is less ideal), sit, and move around with edit. I could actually move. It was amazing. I actually wasn't having huge horrible problems with lag because of it, and it only occasionally popped back after moving.

(Misleading ARC is a peeve of mine as well- especially when people randomly quote the numbers that are pretty arbitrary. I fear it's another case of the Lindens giving an imperfect tool that people don't understand enough to be able to use well to the degree it is helpful.)

August 24, 2008 9:04 PM  
Blogger Miriel Enfield said...

Ana, I disagree with Gwyneth Llewelyn's assessment of the lag attachments generate. I've tested various attachments, checking my frame rates and number of triangles drawn, and attachments are genuinely laggy.

Allegory, I tried to find the red boxes and couldn't. I had a hard time finding stuff in general at Hair Fair.

I fear it's another case of the Lindens giving an imperfect tool that people don't understand enough to be able to use well to the degree it is helpful.

I kind of wish we hadn't gotten it, period. Few people understand it, but they think they do, and it leads to a lot of obnoxiousness.

August 24, 2008 11:22 PM  
Blogger Allegory Malaprop said...

I found the layout a headache, it took me a fair bit of waiting until my map would open to try to figure out where I was for anything but the perimeter. At least I was just going for random browsing, not looking for anything in particular, as I think I would have been even more frustrated then. The box thing did mean I could actually go through and see it, instead of going for 5 minutes and then leaving because the lag was just too unbearable(I'm on a laptop that's a couple of years old....so I'm sure you can imagine how much well attended events tend to encourage me to _not_ attend). So long as I was in build enabled areas, I could go around on a box of my own, and would hop off when I found a red one, so I would be "safe" everywhere.

I kind of wish we hadn't gotten it, period. Few people understand it, but they think they do, and it leads to a lot of obnoxiousness.

Truer words were never spoken. To the degree that it is helpful, common sense should have the same effect.

August 25, 2008 1:19 AM  
Anonymous Anonymous said...

I think what the main concern is, and pardon me if I am wrong. But the more scripts you have attached, the more prims you have attached, the harder the sim has to work to keep itself going. Removing as much of said items helps the sim lighten it's load a little bit. Hence the low sim fps. It would make a difference on the sim in general as it's already working double time to render the avi's and the designers goods. As far as I am aware, if people would detach, detach, detach.

BTW....I don't use that Arc thingy. Never made much sense to me.

Misty

August 25, 2008 4:14 AM  
Blogger Miriel Enfield said...

Allegory, I hadn't noticed that build was enabled. I'll have to do the box thing if I decide to go back (and I may not; nothing I've seen in blog pictures has caught my interest).

Misty, I think you in fact mistaken, at least about a few things. The sim doesn't render stuff -- I don't even think prims cause a load on it. Rendering is done by your computer. Scripts do cause server lag, but not very much. Hair Fair is so packed that AOs may actually cause problems (one of the few cases, I think, where they actually will), but I don't believe other scripted attachments would be much of an issue.

Detaching is still a good policy, of course. :)

August 25, 2008 8:04 AM  
Anonymous Anonymous said...

Doesn't the sim have to 'read' the avi's on the sim, what they are wearing, etc? Maybe render is not the right word?

temp rezzers, many guns/weapons, CSS HUDS, AO's (as you mentioned)...I had always thought they caused server side lag aka sim side lag the gives the low sim performance?

I know you can't compare a full sim with a open space...but if my scripts are running too high on my open space (animated animals KILL me), they start to cause sim side lag, I drop from a pretty standard 45 sim FPS down to 10 sim FPS while my own personal FPS stays around 30ish. I remove those scripts and suddenly, my Sim starts to behave. I've rezzed into places asking for the MystiTool to go to sleep because it's a scripted object that pulls on the sims resources. Maybe it's because you get 20 avi's with it, like an AO...it starts affecting the sim stats?

Which is most likely why so many people are confused about what does and doesn't cause lag (and yeah, that includes me LOL).

Misty

August 25, 2008 9:43 AM  
Blogger Miriel Enfield said...

Doesn't the sim have to 'read' the avi's on the sim, what they are wearing, etc? Maybe render is not the right word?

"Render" isn't. :) Rendering is the process of turning the 3D data into an actual picture. However, the sim does have to keep track of avatars and objects, so attachments very likely do cause load, now that I think about it. I'm not sure how much load they'd cause, though, as I have yet to find an authoritative guide to server lag.

temp rezzers, many guns/weapons, CSS HUDS, AO's (as you mentioned)...I had always thought they caused server side lag aka sim side lag the gives the low sim performance?

One of the nice things about being an estate manager is that you can see script times. It's recommended that you start cutting back on scripts if the time goes over 25 ms. Most scripts take up only a teeny tiny fraction of that. My vendors, for instance, take around 0.030 ms when someone is ordering, and each script takes around 0.003 ms when nobody is. Even AOs, which are quite a bit slower than other scripts, have only tended to take around 0.090 to 0.135 ms.

In addition, what's supposed to happen (according to the LSL wiki, anyway) is that each sim allots a certain amount of time for scripts. If the scripts go over that, what happens is that each script gets less time; the sim doesn't start cutting into the time it uses for other things. The wiki could be wrong, of course.

Even if it is, though, the script time numbers I've seen just don't support the idea that scripts are a big drain on a sim. Unless the script time numbers are wrong or misleading, under typical conditions, a sim shouldn't have issues with scripts. (Hair Fair, of course, is not a typical situation.)

I dunno why your animals would be so slow, though. If they're animated, maybe it's all the object updates, rather than the scripts themselves?

August 25, 2008 11:07 AM  
Blogger Sirahal said...

I actually found hte box thing, as mentioned by Allegory, to be incredibly annoying. When I was there yesterday people were blowing it WAY out of proportion, building their own and such (I even had a group pass by me on a COUCH!)

I was also annoyed with the idea because I kept running into boxes that were discarded, or would have them impeding my view as i tried to look at things.

It's a cool idea, sure, and might work if people had the curtosey to use it properly, but it pulled my experience down a bit.

August 25, 2008 5:43 PM  
Anonymous Anonymous said...

ooh..it's all starting to make sense now and ty so much for taking the time to explain. I'm not really sure about the animals and why they knock my open space down. I have the EM rights and look at scripts running often and they are always the culprit except when SL is being funky..then it's just about anything and I ignore it until the grid levels off. However, they don't seem to cause much of a problem on the adjacent regular full sim. Maybe it's a combination of everything including open space, 1/4 power and all that jazz?

In any case, thank you...I learned lot's out of this!

Sirahel, I noticed that when I was there as well. I used a box, there was about four of us on it...we kept it higher then an avi stands and out of the displays...up and out is the only way to be nice. I did run into someone once though. They flew down as I was editing the box over. I didn't know those red boxes were to be used and saw them left all over the place in odd spots

Misty.

August 26, 2008 2:56 AM  
Blogger Miriel Enfield said...

I have the EM rights and look at scripts running often and they are always the culprit except when SL is being funky..then it's just about anything and I ignore it until the grid levels off.

You're actually getting big script times? Weird. Nouveau and Miriel never have those. Nouveau had ~4.5K scripts at one point, and wasn't even close to 25 ms.

August 26, 2008 3:17 AM  
Anonymous Anonymous said...

yes :( some of the animals shoot up to as high as 10 points on "find the script" thingy for about world/em rights area (such a techy term person here) :( Luckily the creator was kind enough to descript some for me and I think I need to contact her again to get the others de-scripted. I honestly think it might be a open space sim problem more then anything else. They just aren't powered like a regular sim.

I usually know if it's SL in general or animals because of what is script sky rocketing. Normally if it's certain items, like the animals, I can either re-set and replace and everything works fine again (but a HUGE pain). If it's SL in general, it's the odd things, like a tree that has two sits attached to it. I let them go and once SL gets a grid-clear...they relax back to normal. I've tried that with the animals, but they just keep plugging up no matter the grid status.

Misty

August 26, 2008 7:03 AM  
Blogger Miriel Enfield said...

Holy crap, there are scripts out there taking 10 ms? I'm stunned.

You may be right about it being an open space thing. I've never seen any scripts in Nouveau or Miriel (both full sims) doing anything remotely close to that. AOs are pretty bad, since they're checking your animations multiple times a second, and even those take way less time.

August 26, 2008 8:12 AM  

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