Round Robin Scheduling Not Power-Efficient

Via_Patrino writes "While having to distribute load between several servers, round robin, or any other technique that balances load equally, is the most common approach because of its simplicity. But a recent study shows that trying to accumulate load on some servers can improve energy efficiency because the other servers will be mostly unused during off-peak periods and then able to make better use of power saving methods. Specially, where load involves lots of concurrent power-consuming TCP connections, which was the case in the study, a new load-balancing algorithm resulted in an overall 30% power savings. Here's the paper (PDF)."

Comments

Equity or efficiency?

[athloi]

Confronted with distributing food rations to hungry orphans, people would rather be fair than efficient, even if it means letting some of the food go to waste, a US study shows.

But the tests demonstrated that most people preferred equity in distributing food -- that all the hungry mouths got fed equally -- rather than an efficiency that perhaps meant that one orphan got almost nothing but also that no food went to waste.

http://news.yahoo.com/s/afp/20080509/ts_alt_afp/ussciencepsychologymoralityresearch_080509123210

This problem shows up in many places.

IT discovers boiler scheduling

[Animats]

Operators of multiple steam boilers have been dealing with this problem for a century. The number of boilers fired up is adjusted with demand, with the need for some demand prediction because it takes time to get steam up. This was done manually for decades; now it's often automated.

The same thing applies to multiple HVAC compressors. Usually there's a long-term round-robin switch so that the order of compressor start is rotated on a daily or weekly basis to equalize wear.

More and more, IT is becoming like stationary engineering.

Re:IT discovers boiler scheduling

[somersault]

Similar idea to modern fuel efficient engines shutting down cylinders when you're idling as well (probably oversimplifying there but you know what I mean)

Re:Logical conclusion

[MozeeToby]

We've been sacrificing computing power for efficiency for years. New Server CPUs tout thier energy savings atleast as much, and quite often more than they tout their computational power. As electricity gets more expensive and data centers continue to grow this trend can only continue; it's simply too expensive to a warehouse full of server racks unless you focus on efficiency.

I'm waiting for the first company to put a data center a few hundred feet under water, where the water temp is low. You'd be surrounded by the worlds biggest heat sink. The environmentalists would have a hissy fit but that's never stopped industry before, and of course you could argue that you are saving electricty on cooling.

Re:Logical conclusion

[Anonymous Coward]

You aren't sacrificing speed as long as you have properly benchmarked your servers, and understand where the performance hockeystick starts.

Apply a connection limit slightly below the performance hockeystick in your load balancers / content switches and you will get maximum power utilization with minimum performance impact.

One other way I see customers getting maxim utilization out of their servers is by using dynamic resource schedule and vmware esx to move virtual servers around behind a load balancer. At this point your load balancer can be set at round robin (or optimally least connections) and you can use VMware to realize the cost savings of running at 90% utilization vs 30% utilization.

BigIP

[ZonkerWilliam]

BigIP's can use round robin and use prioritizing, in other words one server receives the most connections over the others. So how is this new?

Soccer moms and scheduling.

[viking80]

14 soccer moms are taking the team of 14 kids to a game. They have two options:
A. Spread the kids among all the cars, and drive all the cars (14 cars)
  or
B. Fill up a car, and send off. Repeat until done. (6 cars)

What is more energy efficient?

Soccer moms have solved this without statistical analysis or engine torque curves.

Re:Soccer moms and scheduling.

[Culture20]

Parent post has it all.
Car analogy? Check.
Soccer Moms? Check. Check. (no mention of how many are single though)

But... a lot of soccer moms don't care. They're busy with their other kids and errands too (each server runs more than just apache), so they want the flexibility of driving their own car. Show me a website where the hardware is designed to be energy efficient, and I'll see a site that can't handle a good slashdotting.

Re:Soccer moms and scheduling.

[wombert]

I believe your calculations are wrong. It's understandable, though, since soccer parenting is a fairly unique branch of mathematics.

First off, you're assuming a standard car with 1 adult driver and 4 passengers; instead, you should be using an SUV with a capacity of 6-8, including driver.
(Result: 4-5 vehicles)

Next, you have to consider that not all parents will attend every game. The primary reason that soccer moms drive SUVs is that they must occasionally transport several of their child's teammates to a game (or, worse, to practice!) when their turn comes up in the rotation. Therefore, you only need enough SUVs to cover the number of child passengers, and the number of adults will follow.
(Result: 2-3 vehicles)

However, you might recall that the other reason that soccer moms drive SUVs is that they often have additional children that have not yet reach sports playing age, and must be transported along with the parent, in a car seat (which, in the case of a standard car, would reduce passenger capacity by at least 20% by rendering the back center seat useless.) Assume that approximately 1 in 3 soccer moms have an additional child to transport, and the child adds to the overall passenger count.
(Result: 3-4 vehicles)

Finally, realizing that the overloaded schedule and priorities of child + parent create scheduling conflicts, it is impossible to get optimal performance. At least 1 child per SUV will be late, leaving a seat empty and requiring another parent with car to tranport them.
(Result: 6-8 vehicles)

The result is a range of possible values, but your initial calculation of 6 vehicles is optimistic at best.

Cooling.current == Server.current

[cabazorro]

Here is the solution. In the winter run your web farm in the North hemisphere. In the winter migrate to the South hemisphere. Run it in basements of large apartment complex. Charge for the heating. Heating oil is going up the roof.