UT theoretical chemistry code forum

Hi,

I have 7 computers, all crunching for eOn. My fastest one is a Core i7 running Windows 7. Other one are Core2Duo or P4, all running Linux. My i7 computer is taking almost twice the time to calculate WUs. How come? This computer is 1-2 years old and the other ones are more like 5-6-7 years old. Is there a good reason for the i7 to take so much time? Thank you!

Sometimes project appications run faster on one OS than they do on another OS but I doubt that can explain a factor of 2X.

Check to see if your i7 is down-clocking due to overheating. Have you blown the dust out of the heatsink cooling fins lately?

Are you running other projects too or just eOn? If just eOn and if you have HT enabled on the CPU then you will have up to 8 instances of the same application running simultaneously, a condition which frequently leads to huge slowdowns due to the fact that the 8 applications are competing for the same resources. You can remedy that situation to some extent (but not completely) by running a mix of various projects but bear in mind that 4 real cores is just 4 cores and turning them into 8 via HT doesn't give you 8 real cores, just 8 virtual cores. You can never get 2X as much production by turning on HT though you can often get more than 1X production if conditions are right. There are 3 possible scenarios:

1) You use HT to run 2X as many threads but each thread takes 2.2X as long to complete. In this scenario you are actually losing production. This scenario often happens when running 8 instances of the same application simultaneouly.

2) You use HT to run 2X as many threads but each thread takes 2X as long to complete. In this scenario you are neither losing nor gaining production.

3) You use HT to run 2X as many threads but each thread takes 1.8X as long to complete compared to time required with only 4 threads. In this scenario you are gaining production. This is the only scenario in which using HT has a real benefit.

Hello cola,

Thank you for replying. I disabled HT because I'm using a 3D application on the same computer and it is often not using multiple threads, so I prefer using a "full core" than half of it. I'm taking very good care of the computer, so the fans and vents are cleanup on a regular basis. The OS could be an important point. I may be that eOn is working faster (or just better) on Linux than on Windows 7. I was just surprised that even if the OS is not the same, some P4 were getting much better results than an i7, which is not using HT, so which is using full cores.

I guess there is nothing to do on my side to change that situation, but I was wondering why I'm seeing this.

It's good that you keep your computer clean but there are other factors that can contibute to overheating. For example, if the heatsink does not make proper contact with the CPU it will not conduct heat properly. The CPU will then overheat and to protect itself it will adjust the clock frequency (and perhaps voltage) downward which slows the CPU down so it produces less heat. That happened to me once and after I fixed the problem the computer ran much faster.

It is a good idea to install diagnostic software such as CPU-Z which reports temperature, voltage and clock speed to see if the CPU is running at the normal clock frequency and voltage. Yes, sometimes apps run faster on Linux than they do on Windows (and vice-versa) and perhaps P4 can run some apps faster than i7 but I have difficulty believing those two things together can cause the big difference in speed that you are seeing. I strongly suspect your i7 is not running at normal speed but of course the decision to check or not check is entirely up to you :-)