Thinking about a CPU upgrade - running the numbers for power and Passmark

[wisem2540]

I currently have a 95w Phenom 1045T.  In a perfect world, it would use very little power, but have the ability to do so if needed.  Here is what I have come to understand...please tell me if I am wrong about something...

 

1.  Plex performance largely depends on a CPUs passmark score (1045T is 4,897)

 

2.  High Passmark typically correlates to high wattage, which means more power usage.

 

3.  Even a high Watt CPU will run at very little utilization most of the time, therefore consuming very little power.

 

4.  The difference between a 65w and a 125w CPU (as an example), even under 100% load 24/7 would only be 60W or about 60 dollars per year, which is about 5 dollars a month.  (which would never happen)

 

So, if all of the above things are correct....  Is CPU power usage really a valid concern?

[garycase]

1.  Plex performance largely depends on a CPUs passmark score (1045T is 4,897)

 

Plex by itself isn't very CPU intensive, but if it needs to transcode a media file, then it does indeed use a fair amount of CPU "horsepower".    The rule of thumb is that you need ~ 2000 PassMarks per stream to transcode.    So your CPU should be able to play two transcoded streams.

 

2.  High Passmark typically correlates to high wattage, which means more power usage.

 

No.  The PassMark score simply shows how much power a CPU CAN provide.    It's true that as the CPU utilization goes up, so does the power usage ... up to the maximum power the CPU will use.    But there can be significant differences in the "horsepower" of a CPU vs. the power usage.    For example, a Xeon E3-1275L has a TDP of 45w, yet scores 8665 on PassMark ... i.e. nearly double the power of your CPU while drawing less than half the power.    The Intel CPU's are in general far more power-efficient than AMD.

 

 

3.  Even a high Watt CPU will run at very little utilization most of the time, therefore consuming very little power.

 

True, but this also depends on the efficiency of the chipset and the power characteristics of the CPU.  In general, an Intel Core-architecture based system will run a MUCH lower idle power consumption than AMD systems will.

 

 

4.  The difference between a 65w and a 125w CPU (as an example), even under 100% load 24/7 would only be 60W or about 60 dollars per year, which is about 5 dollars a month.  (which would never happen)

 

The difference would be higher than that, as when you're consuming that much more power you're also generating more heat, so it will cost more to adequately cool the system (more and higher-power fans), and the supporting electronics will likely be drawing more power as well.    But the general idea is correct ... an extra $5-$10 /month is all you're likely to spend in areas where energy costs are modest => Your cost figures seem to be based on about $0.12/kwh, which is a typical cost in the US - but it can be FAR higher in some parts of the world (and even in the US).

 

 

...  Is CPU power usage really a valid concern?

 

That's entirely a personal decision.    Clearly it's unlikely to make enough of a cost difference to be a significant factor for many of us, the same can be said for many other products we have.    Do you care about the SEER rating of your home's air conditioning systems?  ... the fuel economy of your cars?  ... etc.    The more efficient choices often cost significantly more, so it's not always clear that the ongoing operational savings is worth the higher cost from a purely economic standpoint.    But many of us just like to know that we're being as efficient as we can -- whether it's in our PC, our transportation, or our home energy consumption.

 

[wisem2540]

Gary,

 

Thanks so much for your thoughtful reply.  It is very much in line with my thoughts on the matter.  My very next question was what CPU could give me a high passmark and low TDP and you answered it with a Xeon E3-1275L

 

But, that CPU alone appears to be north of $350 dollars.  Going back to our original power discussion, sure I could transcode more plex streams, but id have a break-even point on power usage in 4-6 years....which is a long time.

 

Can you answer one more question for me?  Does passmark relate to VM performance somehow?  I have had ideas for a long time to replace many of the PCs in my house with VMs hosted on unraid.  Again, this would be purely to save on power and hardware costs, but Id want to make sure I had plenty of cycles to handle the needs.  Would you focus more on a bechmark like Passmark, or more on Core Count?

 

This is call coming about because my unraid rig has only 8GB of RAM and with crashplan running, its almost maxed.  So I need a board that will support 32-64GB.  So I am trying to decide whether to replace the board and re-use the CPU, or make the switch to Intel.  I have a relationship with intel that could net some significant savings on CPUs

 

Thank you again.

[garycase]

PassMark measures the overall "horsepower" of a CPU ... and that's definitely a factor in the performance of virtual machines (along with the hardware support that vt-x and vt-d provide).

 

Cores are also significant, since they make it more efficient to distribute that "horsepower"  (even extra threads supported by hyperthreading are helpful, since they make context switching so much more efficient).

 

But probably the biggest factor in VM performance, given that you have "enough" CPU power, is having enough memory so that your VMs are causing excessive page faults.    If you plan on running several simultaneous VMs, be sure you have enough memory that UnRAID will have plenty of memory even after all of the memory your VMs need has been allocated.    16GB is usually enough; but 32GB clearly provides more "headroom" and may be necessary if you're running more than 2-3 VMs.

 

When you consider the total cost of your hardware, spending a bit more for a high-end CPU really doesn't make much difference -- it's an expensive you'll rapidly "forget" .. but you'll definitely like the performance it provides as you get used to its capabilities.    That CPU costs half of what I plan to use for my next system    [A hex-core E5 series Xeon E5-1650v3]

 

[wisem2540]

Gary,

 

I am looking at a Xeon E5-2418L but the board selection seems limited with this socket.  Am I missing something?

[garycase]

I suspect it's fairly difficult these days to find a Socket 1356 motherboard, so I'm not surprised.

 

If you want to go with an E5 series Xeon, I'd definitely use a Socket 2011 board and CPU.    Far more CPU choices; and a much higher performance motherboard.

 

[French-Guy]

Gary,

 

Thanks so much for your thoughtful reply.  It is very much in line with my thoughts on the matter.  My very next question was what CPU could give me a high passmark and low TDP and you answered it with a Xeon E3-1275L

 

But, that CPU alone appears to be north of $350 dollars.  Going back to our original power discussion, sure I could transcode more plex streams, but id have a break-even point on power usage in 4-6 years....which is a long time.

 

Can you answer one more question for me?  Does passmark relate to VM performance somehow?  I have had ideas for a long time to replace many of the PCs in my house with VMs hosted on unraid.  Again, this would be purely to save on power and hardware costs, but Id want to make sure I had plenty of cycles to handle the needs.  Would you focus more on a bechmark like Passmark, or more on Core Count?

 

This is call coming about because my unraid rig has only 8GB of RAM and with crashplan running, its almost maxed.  So I need a board that will support 32-64GB.  So I am trying to decide whether to replace the board and re-use the CPU, or make the switch to Intel.  I have a relationship with intel that could net some significant savings on CPUs

 

Thank you again.

I know it’s a few month old thread, but I’m interested by what you want to do:

I have had ideas for a long time to replace many of the PCs in my house with VMs hosted on unraid

So let say I build a new Unraid server, and want to run (virtualize?) a Windows 10 machine (client?) for example (a simple one, just to do email, web browsing, youtube, facebook…..so light stuff)

How would this work exactly? What that client would consist of? Just a keyboard and monitor?

 

Thanks