2 identical processes - different speeds

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I run two identical processes. One of them requires 90 minutes to complete. The other takes 150 minutes. I expected them to be the same, and am unsure what the problem is.

What I have tried:

I did the above experiment on a different machine and the running times are more as expected (90 minutes each).

Posted 26-Sep-24 0:16am

LF FF

Updated 26-Sep-24 4:25am

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0x01AA 26-Sep-24 10:56am

Define 'identical'. I assume you don't mean the one and the same executable?

LF FF 26-Sep-24 11:22am

It can be two instances of processes of the same executable (doubleclick/start the same .exe twice, for example), or two different executables (doubleclick/start different .exe files from the identical source code). I have tried both with the same results.

0x01AA 26-Sep-24 12:03pm

Do you run them in the same time? If yes, can you maybe see (in task manager) that one of them consumes the whole CPU in the first 60 minutes?

LF FF 26-Sep-24 12:36pm

Thank you. Yes, they are run at the same time, and they are started at the same time. I notice one of them is consistently higher in terms of the % CPU usage but not by much (maybe a 1-3% difference at most). Each show about 10% CPU consumption. The one which takes longer may sometimes drop to 9% or so. Hard to characterize as they fluctuate. I am now wondering if there a way to force the CPU consumption to be higher in one or both, to, say, 20% each? There are a bunch of other processes (probably Windows and vendor-specific processes to the laptop, I hesitant to mess with those for now as the total CPU consumption is shown as 20-50%).

As I research this, I see that Processor Affinity and CPU Priority can be manually set in Task Manager, but I am also wondering if the way CPU is consumed by the app can be set in the C#/.NET.

siliconvideo 26-Sep-24 12:08pm

Need more information, Are the 2 processes running in parallel or sequential? Are they crunching the same data set? Is there a memory limitation (if one process needs more memory, it could be swapping to the hard drive more slowing everything down.) What are the other processes running during your test runs. How do the different machines compare? ...

LF FF 26-Sep-24 12:13pm

They are running identically on the machines, i.e. in parallel on the same data sets. I set it up this way so that the only difference would depend on machine. Machine difference? Although not identical machines, they are set up similarly. The main difference is that tbhe one that is exhibiting the issue has more RAM.

siliconvideo 26-Sep-24 16:02pm

Normally I'd let the OS handle the priorities, you should not have to. Are they both working on the same data set or is the 2nd instance working with a copy of the 1st data set. Possible collision if both instances are trying to access the same data set. What is the data set? text file, sql....?

LF FF 26-Sep-24 16:38pm

Text file, but I assume it might not be related to this. The reading of the text files occur infrequently and when it occurs, it is near instantaneous. Not enough to account for a 30 minute discrepancy.

siliconvideo 26-Sep-24 16:57pm

Does the application close the text file immediately after grabbing a chunk of text or does it keep it open until it is totally done with the file. If it keeps it open till it's finished with it the 2nd instance is probably just in a while forever do nothing loop until it can open the file.

LF FF 26-Sep-24 17:05pm

Nice thought, but the text file is immediately closed.

siliconvideo 26-Sep-24 17:21pm

Without looking at the code I am out of things to suggest. Usually issues like this are apps fighting over the same resources or one app is constantly being swapped back and forth to the hard drive. Let us know if you find the cause. Good luck.

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OriginalGriff · Accepted Answer · 2024-09-26T19:44:00

We really can't tell - we have no idea what your app is doing. But ... the most likely thing is resource locks. For example, if the app attempts to write to a file then only one of them can access it at a time - so the other has to wait for the first to close the file and then continue.

So start with your code and either use the Stopwatch class to monitor in real time (to separate log files) where one instance is running slowly compared to the other then narrow down on those sections, or look closely at your resource usage.