[Galaxy S 4 i9500 Original Android Development] lukair1983:
Have a question regarding testing GPU undervolting, but first a small feedback to Andrei.

I got a third time (just to be clear, it is very rare; I'm using the Perseus Kernel for almost 2 weeks now, and I only noticed it happen 3 times) a strange occurance, namely the GPU frequency went to the max (700 MHz) by itself. Meaning I didn't change it manually, I was just running other application (which was on top), and later on, when I opened Synapse I noticed it had the max frequency for GPU set to 700 MHz. It happened just now with my stress testing with StabilityTest, and also 2 times with a NDS emulator.

Now getting back to my question about GPU testing.

So far I've noticed the best test is really just using the phone, and especialy leaving it for a while(best an hour or even couple hours) so that it's deep into sleep. After waking up I got crashes most of the time if the voltage was too low.

I'm testing now a 775 mV at the lowest GPU frequency, and so far so good. No crashes since couple days, I also did 3d Mark, GFX Benchmarks, Antutu, all passed, no crashes.

I decided to try and stress test the GPU with StabilityTest, and it gives me some strange results. When running it for a little while (under an hour) it shows no gpu errors, but yesterday I got gpu errors at the over 1h mark (around 1h 15m). So today I tried again, and the same thing happened, at shortly after 1 hour mark.

Ok, I went back to the stock setting of 950 mV (for 177 MHz, since that's what I'm testing atm), and guess what. Same thing happened, although at the 25th minute mark (but truth to be told, I exited the app unintentionaly just prior to it, when it was already at 50th minute, so that might have some toll).

So after that I tried to up my max frequency of GPU to the stock on 480 MHz, same thing. 1h 2 minutes in, got the same screen with gpu errors.

The problem of mine is that it shouldn't (well unless the chip is unstable originaly) show any errors at stock settings.

So there are only 3 possibilities:

a) Either the StabilityTest application has an internal bug that damages the results after some time

b) My chip is broken, hence errors at the stock values

c) Perseus Kernel has something to do with it (maybe it is not compatible with the app completely, and the app is getting not true results and interpreting them as gpu errors, when in fact they are not)

There is one thing though. Every time it happens, I get the same message (Preparing Scene, Please wait) as when the test is loading. I added the screenshot as attachement, which leads me to the option a) as the biggest possibility at the moment.

Since only this app shows gpu errors (no crashes whatsoever), and I have no other problems at all, I'm willing to assume it's just a bug and shouldn't worry about it. But I was wondering if anybody did the same kind of testing and noticed something similar?

//Edit

Ok, I see the problem with stress testing GPU or CPU on Android is widely known:

http://xdaforums.com/showthread.php?t=1029035

Basicaly, I see there is no good method enough (like running Prime95 on PC for a long time that gives very high probability of a stable system) to stress it, and it becomes really sometimes a guess work, unless someone has a freeking loads of time to test every single frequency for a week+.

But anyways, sharing this information to others with similar dillemas, that StabilityTest doesn't really test realiably which I expierienced myself, nor any other Graphical Test. For example I was able to pass the test that was running for almost an hour, while a simple deep sleep would crash my phone when I woke it up.