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  Are ‘Second Life’ Avatars Energy-Suckers?  
Posted 2006-12-05 by Tony Walsh
Rough Type's Nicholas Carr responds to my question "is Second Life sustainable?" Carr informally juggles some numbers related to Second Life's average concurrent population and power consumption by the servers running the virtual world, comparing power usage per avatar to power usage per human being. He finds that "an avatar consumes a bit less energy than a real person, though they're in the same ballpark." It's great that Carr took a stab at this, but it would be better if Linden Lab could give us some actual power-consumption data to work with.

If Carr's model is accurate, I'm a bit surprised that avatars consume even close to the amount of power we humans consume. Actually, if you consider that it takes a human to operate an avatar through his or her own computer, the power-consumption is even higher. That's one human running their own computer to operate an avatar existing on Linden Lab's servers.
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Comment posted by AndrewLinden
December 5, 2006 @ 1:13 pm
Sorry, I don't have any numbers for you, but Ian Linden might be able to supply some. Send him an email, he might respond.

When you stand in the roaring gale between two rows of racks of SL servers the energy consumption issue invariably occurs to you. The good news is that the Watts/CPU ratio is going down over the years. I know this is true because we used to be bottlnecked by the Amps available in each rack, and were unable to fill a rack completely, however we now fill each rack to the brim, and have doubled the CPU/server ratio at least twice.
Comment posted by Tony Walsh
December 5, 2006 @ 5:57 pm
Thx, Andrew. Does Moore's Law apply to power efficiency? (semi-rhetorical question)
If so, then any ecological footprint issue will diminish rather than getting worse. On the flipside, I can only see SL's processing demands increasing over time. So we'll probably be able to fit more CPUs in a rack (better efficiency over time), but we will probably also need more CPUs, or faster CPUs (greater power consumption overall). Or something. This isn't really my area of expertise... I'll ping Ian...
Comment posted by Prokofy Neva
December 5, 2006 @ 6:49 pm
Wow, this sort of thing is bound to get all the politically-correct juices flowing, before you know it, it will be considered as evil to have an avatar as it is to drive an SUV!

I'd like to see this discussion not in terms of per-person usage, or "Brazil" or whatever, but more concrete examples like: "the server far powering SL with 5,000 servers can light up the Empire State Building for 90 days" or "can heat a village of 3,000 for year" or something concrete about what you use the energy *for*.

Then we can nicely turn it into one of those "cloth vs. disposable" debates. Yes, disposable diapers consume landfills and despoil the environment. But the diaper trucks driving to your house or your washing machine also consume energy washing the cloth diapers. Same idea. Yes, a kid in a dorm room these days probably consumes enough electricity to power a small third-world village. But he's not watching TV or driving around or shopping at the mall burning gas if he's online. So maybe he could be out there powering 3 villages with all his first-world activities but avatars have actually helped him save the third world by reducing his overall footprint on our planet.
Comment posted by Prokofy Neva
December 5, 2006 @ 6:51 pm
*even if you add in the power consumed in keeping the server farm powering his avatar and world -- because then there's less TV and other consumption.
Comment posted by AndrewLinden
December 5, 2006 @ 7:16 pm
I think there is a trend that is similar to Moore's, when it comes to Watts/Avatar but I'm not sure what the half-life would be nor how long it would continue.

It turns out there is room for optimization in our software that could certainly double the avatar and object density for the same CPU cycles, but it will take work to get there. In a sense, I'm working on that project right now, since I expect to make some incremental contribution toward that goal when I'm done with my current task. Various other projects will contribute more or less to the effort.

One problem with SL is that a region's simulation continues as fast as it can even when the region is empty. However, I had two ideas recently about how we might be able to deschedule empty simulator processes so that they still run, but on far fewer CPU cycles. Maybe someday I can find the time to work on them.
Comment posted by Prokofy Neva
December 5, 2006 @ 8:11 pm
<a region's simulation continues as fast as it can even when the region is empty

So when a tree falls in the forest, it *can* be heard.

Of course, if you deschedule it, the question is -- will it power back up quickly when its owners or inhabitants log on??
Comment posted by AndrewLinden
December 5, 2006 @ 8:56 pm
Sorta. When a tree falls in an empty region it would make a noise, but no one would hear it.

By "descheduled" I don't mean "not running", since one never knows what the scripts are doing with no one there. Perhaps they are measuring wind speed and sending emails every hour. Instead I mean "given a lower process priority in the kernel's scheduling system" via the "nice" command. This would free up CPU cycles for other stuff and would theoretically make the CPU use less power. I think switching the runtime priority could be done in an instant, so bringing it back to normal priority could be done the moment someone looks into into the region.

It occurs to me now that even if I were able to reduce the average power consumption of the simulator machines by a whopping 10% it wouldn't save LL any money since I don't think we pay by average power consumption, but by the gauranteed peak power dedicated to each rack. That is, I think the power costs are more or less fixed.

That doesn't mean that it shouldn't be explored. There would be other small benefits since each machine is running a lot of other services at the same time on the spare cycles (apache, squid, a mysql connection, and a bunch of misc stuff) and we've got ideas about other jobs we'd like to distribute to the cloud. It is fun to think about. We'll see what happens.
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