Remember the movie National Lampoon’s Vegas Vacation, when gambling fever consumes Chevy Chase’s character, Clark W. Griswold? He goes on a losing streak to beat all losing streaks while his son, Rusty, wins four cars by playing the slot machines. Maybe Clark would have done better if he had read Probability For Dummies! In this article, you discover the basic ideas behind slot machines and how they work, so that you can get past the myths and develop a strategy based on sound probability.

Understanding average payout

When casinos advertise that their slot machines pay out an average of 90 percent, the fine print they don’t want you to read says that you lose 10 cents from each dollar you put into the machines in the long term. (In probability terms, this advertisement means that your expected winnings are minus 10 cents on every dollar you spend every time the money goes through the machines.)

Suppose you start with $100 and bet a dollar at a time, for example. After inserting all $100 into the slot, 100 pulls later you’ll end up on average with $90, because you lose 10 percent of your money. If you run the $90 back through the machine, you’ll end up with 90 percent of it back, which is 0.90 x 90 = $81. If you run that amount through in 81 pulls, you’ll have $72.90 afterward (0.90 x 81 = 72.90). If you keep going for 44 rounds, on average, the money will be gone, unless you have the luck of Rusty Griswold!

How many pulls on the machine does your $100 give you at this rate? Each time you have less money to run through the machine, so you have fewer pulls left. If you insert $1 at a time, you can expect 972 total pulls in the long term with these average payouts (that’s the total pulls in 44 rounds). But keep in mind that casinos are designing slot machines to go faster and faster between spins. Some are even doing away with the handles and tokens by using digital readouts on gaming cards that you put into the machines. The faster machines can play up to 25 spins per hour, and 972 spins divided by 25 spins per minute is 38.88 minutes. You don’t have a very long time to enjoy your $100 before it’s gone!

The worst part? Casinos often advertise that their “average payouts” are even as high as 95 percent. But beware: That number applies only to certain machines, and the casinos don’t rush to tell you which ones. You really need to read or ask about the fine print before playing. You can also try to check the information on the machine to see if it lists its payouts. (Don’t expect this information to be front and center.)

Floor ‘heat maps’ for over ten metrics by Seat, Bank, and Zone. Add geographic visualizations to casino patron and hotel guest data. Perform visual game preference analysis on casino patrons for VIP events, groups, and promotions. Provide up-to-date visual reporting of slot machine issues to techs and vendors. Customer demand for slot machine play in particular seemed to be saturated. In the fall of 2011, this thought had been on the mind of Elliott Daradich, SaskGaming’s Director of Slots for nearly 17 years. On board since the casino's inception, Elliott witnessed the development of the business into an increasingly dynamic environment.

Implementing a simple strategy for slots

Advice varies regarding whether you should play nickel, quarter, or dollar slot machines and whether you should max out the number of coins you bet or not (you usually get to choose between one and five coins to bet on a standard slot machine). In this section, you’ll find a few tips for getting the most bang for your buck (or nickel) when playing slot machines.

Basically, when it comes to slot machines, strategy boils down to this: Know the rules, your probability of winning, and the expected payouts; dispel any myths; and quit while you’re ahead. If you win $100, cash out $50 and play with the rest, for example. After you lose a certain amount (determined by you in advance), don’t hesitate to quit. Go to the all-you-can-eat buffet and try your luck with the casino food; odds are it’s pretty good!

Choosing among nickel, quarter, and dollar machines

The machines that have the higher denominations usually give the best payouts. So, between the nickel and quarter slots, for example, the quarter slots generally give better payouts. However, you run the risk of getting in way over your head in a hurry, so don’t bet more than you can afford to lose. The bottom line: Always choose a level that you have fun playing at and that allows you to play for your full set time limit.

Deciding how many coins to play at a time

When deciding on the number of coins you should play per spin, keep in mind that more is sometimes better. If the slot machine gives you more than two times the payout when you put in two times the number of coins, for example, you should max it out instead of playing single coins because you increase your chances of winning a bigger pot, and the expected value is higher. If the machine just gives you k times the payout for k coins, it doesn’t matter if you use the maximum number of coins. You may as well play one at a time until you can make some money and leave so your money lasts a little longer.

For example, say a quarter machine pays 10 credits for the outcome 777 when you play only a single quarter, but if you play two quarters, it gives you 25 credits for the same outcome. And if you play the maximum number of quarters (say, four), a 777 results in 1,000 credits. You can see that playing four quarters at a time gives you a better chance of winning a bigger pot in the long run (if you win, that is) compared to playing a single quarter at a time for four consecutive tries.

The latest slot machine sweeping the nation is the so-called “penny slot machine.” Although it professes to require only a penny for a spin, you get this rate only if you want to bet one penny at a time. The machines entice you to bet way more than one penny at a time; in fact, on some machines, you can bet more than 1,000 coins (called lines) on each spin — $10 a shot here, folks. Because these machines take any denomination of paper bill, as well as credit cards, your money can go faster on penny machines than on dollar machines because you can quickly lose track of your spendings. Pinching pennies may not be worth it after all!

I have previously written about analyzing host and virtual machine performance using esxtop. This post will continue to look at how this information can help with troubleshooting performance, and what values indicate a problem may exist.

Troubleshooting Host CPU Performance Using esxtop

When using esxtop to help troubleshoot CPU performance the main metrics to be aware of in relation to the host itself are:

• PCPU USED(%) – The percentage CPU usage per PCPU and the PCPU usage average across all PCPUs.
• PCPU UTIL(%) – The percentage of unhalted CPU cycles per PCPU and the average across all PCPUs.

If a host is suffering from CPU saturation then you should look more closely at the virtual machines running on the host. CPU usage can be lessened by tuning the settings of the virtual machine, for example, increasing memory/decreasing vCPUs. Ultimately though, it may be that the demands of the virtual machines exceed the resources available on the host. DRS will help with this. If DRS is unavailable then you could look to migrate some of the virtual machine workloads off of the affected host. Ensure that, if you are migrating VMs, that it will not cause CPU saturation on the destination host.

Along with ESXTOP, you can also monitor host CPU performance using the charts available via the vSphere client.

Troubleshooting Virtual Machine CPU Performance Using esxtop and vCenter Charts

CPU metrics to monitor when using esxtop to help troubleshoot virtual machine CPU performance issues include:

• %USED – This is the percentage of CPU time accounted to the world. This value can be over 100 as, when viewing the world group for the VM, the value maximum value is the number of worlds in the group (NWLD) multiplied by 100. If the %USED value is high it means the VM is using lots of CPU resource. You can expand the VM’s world group to see what is using the resource. Using the example above, the VM’s world group has 5 worlds, which can be seen expanded in the following example.
• %SYS – This is the percentage of time that the system services are spending on the VM. If this value is high it tends to mean that the VM is experiencing high I/O. Ideally this should be lower than 20%.
• %OVRLP – This is the percentage of time spent by system services on other worlds. When this value is high it is normally an indication that the host is experiencing high I/O.
• %RUN – This is the percentage of total time scheduled for the world to run. %USED = %RUN + %SYS – %OVRLP. When the %RUN value of a virtual machine is high, it means the VM is using a lot of CPU resource.
• %RDY – This is the percentage of time a world is waiting to run. If this value is higher than 10% it means that the virtual machine is possibly under resource contention. Remember that this value is per vCPU world, so for virtual machine with multiple vCPUs you can expect higher values. This is an important metric to pay attention do. Generally you will see higher ready values when you are using multiple vCPUs on a virtual machine, because the VMKernel will try and schedule all the vCPUs close together, which may result in the VM needing to wait before it’s thread can be executed. Ideally you want to see the ready time to be under 10% but best if closer to 5%.
• %MLMTD – This is the percentage of time the world was ready to run but was deliberately not scheduled as it would have violated CPU limits. This value is contained in %RDY. If this value is high then you could increase its limit, adding more vCPUs. This should always be 0 so long as CPU limits are not in place on the VM.
• %CSTP – This is the amount of time the world has spent in the ready, co-deschedule state. This is only applicable for SMP VMs. The scheduler tries to execute on all vCPUs. The %CTSP value is the time the vCPU is stopped from executing whilst waiting for other vCPUs in the same virtual machine to execute/catch up. This value shouldn’t be higher than 3%. If it is generally higher than that then it may be that the VM has too many vCPU.
• %WAIT – The percentage of time a world has spent in the wait state. The %WAIT is the total wait time which includes %IDLE and I/O wait time.
• %IDLE – The percentage of time a world is in idle loop.
• %SWPWT – The percentage of time the world is waiting for the VMkernel swapping memory.

As a memory aid, when looking to memorise these metrics, take a look at my post on esxtop flashcards. Alternatively, you can also investigate virtual machine CPU performance using vCenter charts:

More on %RDY

Ready Time (%RDY) is the amount of time a VM is waiting to be scheduled on a physical CPU. I mention above that generally %RDY should be under 10%. This is true, however the values you see in esxtop may be confusing. This is because how you interpret the values is influenced by how many vCPU worlds the virtual machine has. %RDY is a sum of all vCPU %RDY values for the VM. For example, if a virtual machine has 1 vCPU then it’s maximum %RDY value is 100%, however, if a virtual machine has 2 vCPU then it’s maximum possible %RDY value is 200%. Therefore, whilst 10% %RDY is potentially bad for a 1 vCPU VM, it may not be an issue for a 2 vCPU VM.

For virtual machines with multiple vCPUs, you can use the expand option in esxtop to expand the world group to get a break down of %RDY values for each individual vCPU:

Slot Machines Performance Metrics Inc

High %RDY values can be an indication that the host is under physical CPU contention due to the demands of the virtual machines or that a virtual machine(s) has been overprovisioned/allocated too many vCPUs.

Slot Machines Performance Metrics Tool

If %USED is relatively low, but ready times are high it is a good indication that the virtual machine is over-provisioned. Where possible a single vCPU should be used.

Guest CPU Saturation

If %USED is high then the virtual machine is using a lot of CPU resource. If does not necessarily indicate that there is a problem, but if the Guest’s CPU usage is continually very high then steps may need to be taken to alleviate the problem. There are a couple of approaches to take here. It may be that the virtual machine genuinely is under provisioned in terms of vCPU resources, in which case, adding more vCPUs to the virtual machine will help. Alternatively, there could be a problem with the guest – perhaps a process is taking up all the CPU time due to a fault, or it could be that the virtual machine hasn’t be allocated enough memory, in turn causing pressure on the VM’s CPU resources.