Is one sim per server feasible ?

I'm sure SL would be more expensive but would having only one sim per server a good way to increase performance ? I have no clue. Anyone know ? TIA.

Way back in beta, it was one sim per server. No dual core servers were used back then. Those old machines were retired ages ago.

Current machines (AFAIK) are 4 CPU servers. Each sim runs on one CPU. Making a program use several CPUs at once requires extra work, and sometimes is very complex.

This is hard to say without seeing what they're actually doing, but based on the information I have, I think things would change very little. Without being specifically designed for it a program can't use other CPUs, so a sim can't really take anything away from another other than shared resources like memory, and they probably have enough of it so that this doesn't become a problem.

I asked Torley, on her blog, if having more machines or better machines would help in sim performance.

She replied that no, it wouldn't make any difference.

coco

4cpu's but sharing the same 512 mb of ram, and more importantly the system bus

I've seen how much strain is put on a servers CPU from running a sim. It would be easier on the computer if it didnt have to run as many. BUT then you would have extra expences and more computers filling up LL's warehouse.

Yes, absoluely, it would improve performance. You may have a seperate CPU, but you are still battling for resources (ie, memory) with other simulators.

The question is, is the cost / performance trade off worth it?

My guess would be no, but I don't entirely know how much Linden Lab is paying for their servers.

A better way to look at it, would you rather a weaker CPU on a dedicated box, or a more powerful CPU on a shared box? My understanding is the latter is the prefered way to go.

IIRC, sims run on Opteron servers. Opterons, unlike Intel CPUs don't share the bus, each processor has its own memory controller and connection to the RAM.

my bad

I have a dual CPU box here. In fact that's what I use to run SL.

Dual CPUs make zilch difference to anything that can only use one. The only benefit to have more than one CPU is if you have a program that can split the workload between several CPUs, or run several things at once so that they use different CPUs.

Battling for resources in a server environment doesn't really happen to any significant degree. Yes, having 1GB RAM I could run two processes each taking 600MB and end up with worse performance than running just one, but that's just stupid. If you're running a server seriously you'll have taken that into consideration already. If you have that problem you don't buy another server, you add RAM.


Depends, are you ready to pay about $3500 - $4000 for your island? Because that's about the cash a 4-way box costs.


It depends a lot on the workload. For SL, I'd say multi CPU systems are perfect. They're cheaper than 4 boxes, and performance won't really suffer as you'll be running one process per CPU, each of which will be allocated enough memory not to conflict with anything else. And I'm guessing disk access will be almost inexistent.

Now, something like a heavily used database server wouldn't really mesh well with anything else on the same box. But that's the thing, it depends. IMO SL is just the kind of thing for which this makes perfect sense.

Also, have in mind, that if a 4-way server costs $4000, it doesn't mean that a single CPU server of the same performance would be $1000. You now have 4 cases, sets of fans and heatsinks, power supplies, etc to pay for, as well as more rack space (space in a proper air and power conditioned data center isn't free).

and 4x the maintnace (fans crap out quick)

Last I checked the Sim code was still compiled in a single threaded 32bit form and each Class4 server has 4 instances of the Sim software running with each having an affinity set to one core each. I believe a month ago they started attempting to compile the Sim code in x64 mode (64bit) wich would greatly improve performance. Whether they optimised the code for multithreaded applications as well is unknown.

If I remember correctly, a few months ago I saw a huge embroilment of a discussion between residents and a LL employee swearing up and down that they were infact running on 4 proc boxes (that the class 4 servers have 4 processors). The suspicions were, that LL has infact not been running on true 4 way boxes but infact 2 proc/2 core servers.

Class 4 servers are infact as suspected 2 Proc servers, not 4 proc. I don't care what you say about the matter, but 4 single procs are gonna run faster than 2 procs, dual core or not.

Please see Andrew Linden's post here from just a few weeks ago in SL Answers on 7-20-06:

/139/88/119032/1.html#post1161523

Found it:

/111/2f/66175/1.html#post690056

Lee Lindens' first post to this thread clearly stating that class 4 servers are 4 CPU servers:



And the gigantic thread it is pulled from:

/111/2f/66175/1.html

To refresh my memory I'm gonna scan back through it, because I think LL contradicted themselves in mis-representing what hardware they are using for servers to the general public.

(Just a guess)

One of the major bottlenecks would have to be in the networking between sims in addition to the internet traffic. I wonder... are they using gigabit switches yet?

A "dual core" CPU is nothing more than two CPUs stuck into the same package. In fact they have better performance than what you call a "true dual CPU", as they can talk to each other faster than if they have to do it over a bus.



Absolute statements are dangerous to make. 2 x 2GHz CPUs are a lot faster than 4 x 200MHz ones. Dual core is better than separated CPUs. Some tasks simply don't benefit from extra CPUs. And so on.

If I'm not mistaken, what the servers actually are is Dual Dual-Core Opterons, so they're 2 CPUS with 2 cores each, which is effectively 4 CPUs, but I'm not sure how that pans out for memory access. Also, I believe the servers have 2 GB of memory, so it's 512 per sim, not 512 shared.

So . . . is it correct that more or better machines would not make much of a difference in sim performance? Or is that wrong?

coco

You are correct. We've hit a point of diminishing returns when it comes to sim performance vs hardware.

Would these help?

http://www.nvidia.com/page/quadroplex.html

i would click on that, but you in a diaper is just... you know..

hehe

Stop following me!!

the big problem isn't really performance with shared boxes but that they are harder to configure / program than dedicated boxes, so potential for bugs are rampant!

No kidding sherlock? You do not need to explain to me the differences in the hardware here, I was not asking for that. I am a hardware engineer, no need to go there and I'm not giving you my credentials. You are somewhat incorrect however. You can not fit double the amount of data bandwidth through the same size pipe to the dually's. You can however fit more bandwidth through said size pipe(s) over two single procs, because they are just that, 2 unshared bus. If implemented properly, you would have 2 procs, two unshared banks of ram, etc. I'm talking about data to the procs and leaving the procs over the bus, not what the proc can handle internally. Two single procs using the same available, unshared bus. Sorry, ain't gonna happen until they come out with a double data rate mobo over what they currently have for the dually's to sit on. That's like saying you can cram a 4"x4" square block through a 1" diameter pipe.

What I bolded, and turned red in your statement is the biggest problem, as that does not matter in this situation. It may be true with a standard set-up, but in some commercial server environments, and the way LL is utilizing and singling out each "core" per sim, that is not the case here, they do not need to talk to each other, thus splitting everything up and sharing the proc.

The dual proc dually's LL is using is set-up to run on a shared 1 gig of ram, split 4 ways. That's 512 MB per proc, and if they are running the application as they say they are, that's also cut in half, so 256 MB per proc. Then they share the HD. The app however (simstate files) stay loaded in memory, are running with proc affinity set, and should rarely read/write the HD. As Lee Linden himself said, if it does, you'll know it. It wreaks havoc on the servers performance. Then you've got the issue of network traffic. Maybe the servers are running somewhat fine, but is there a networking bottle neck? Don't think they've ever given us that answer, doubt they ever would.

Following what Lee Linden says, it's 512 per processor. A processor is defined hardware wise as that chip that sits on your mobo. That is your CPU. I know you know that. Think about it, the chip makers have been VERY CAREFUL to not say, "OH LOOKY, buy our chip because it's a Dual Processor Chip!" That would be a false statement and they know it. I'm not here to knock dual core procs, I have them myself, love them, they are faster with most applications, but there is still that bottleneck.

My argument is, they (LL) are running around saying their machines have 4 CPU's, or 4 Processors (both terms have been used). Those statements are not correct, since they are running Dual Processor, Dual Core. There is a difference. You can't fit 2 times the amount of bandwidth over that same amount of pins for that bus. You've got to double the bus to that single processor, and I don't think I've seen that in the mobo market last time I looked.