different result from the same code

[howardhh]

Hi all,

In my program, I use e-core, shared_memory, where I put lots of arrays, but I'm sure the space is big enough.
When I run the code several times, I found that the result each time is different! Do you guys know what will cause this?
Is memory conflict the most possible reason? If so, why this happens? I allocated many arrays in a struct, and didn't use pointer.

Looking forward to your reply! Thank you!

[piotr5]

how did you access the array without a pointer? operator[] is working indirectly with pointers too! so when you use a value that's too big (for example you write the same number as the array was defined with, or you start counting from 1 instead from 0) nobody will notice the overflow and since array-data is uninitialized at start you will use memory that's uninitialized or occupied by something else, maybe on a different core...

[sebraa]

If you expected identical results, and you get different results, then you most likely made a mistake. Unless you explain a bit more what you were up to, all we can do is guess.

[howardhh]

[mikebell]

Is your N odd? If so, you're probably a victim of differing default alignment between the ARM gcc (4 byte alignment) and Epiphany gcc (8 byte alignment).

If it's not that then you still haven't provided much detail on how your code works - e.g. are you running one epiphany core or many? How do you determine the memory address in shared memory for each Epiphany core to work on?

[howardhh]

[piotr5]

if alignment differs, and you initialize from host while using it from e-cores, then alignment and thereby sizeof(Mailbox) don't match between host-program and e-Cores! the compilers fail to understand eachother.

[mikebell]

Without seeing some more of your code it's difficult to know if this is the problem - but from what you just posted it seems possible you are iterating over the same data with each of the 16 cores, so you would get different results depending on timing of when they start, etc.

Maybe push your project up to github or somewhere else public, so we can see everything you're doing?

[sebraa]

[howardhh]

Thank you all for the suggestions. Here is my code:
I'm not familiar with github, so this looks a little disorder...