[HTC EVO 3D] mikeyxda:
Editing it with ES Note Editor (from ES File Explorer) does corrupt the file! Any and all text editors you use on the mpdecision file will corrupt it. I use XVI32 also (small world I guess... great program). But if you use ES File Explorer (ES Note Editor) and you only look at the readable section of the file, of course it will look the same as that part is (mostly) text and it won't get modified. But I guarantee you the file is corrupted if you edit it with ES File Explorer. I just did it myself: start size was 9.7Kb before editing with ES File Explorer, end size after changing nothing but the "userspace" to "ondemand" was 12.01Kb.

If you use a file compare tool like directory toolkit or winmerge, you'll find that even though you only changed "userspace" to "ondemand", there are thousands of changes all over the file. One thing I've learned is that if you use System Tuner and you see that your second CPU is online all the time, you've corrupted the file (unless you used the System Tuner tweak to force both online). If you do the change properly and use XVI32 or another hex editor to only change "userspace" to "ondemand" and that's the only change you make in the file, the second CPU will be offline when you check it with System Tuner.

All that aside, if you just delete the mpdecision file, the second CPU stays online all the time too so I think the effect of corrupting the file is the same as deleting it. I'm currently running my phone with no mpdecision file and it is a hair faster (a few percent) in all the benchmarks but it seems a lot faster than a few percent because apps open snappily, screens scroll instantly, etc. so it feels faster. Battery does suffer but I'm still on the fence as to how much battery life suffers. May run it a few days like this to see.

Now that I've written all this, it looks like a mess so here's a summary:

(1) If you delete the mpdecision file (or rename it), the system can't find it and has no way to follow the special policies on multi-processor performance inside the file. In this case, it appears that the phone runs under some default (manufacturer) settings where the second CPU is online all the time, following the same min/max governor rules as the first CPU. The phone is snappier and benchmarks are slightly improved. Battery life seems affected but not a whole lot. Still testing that.

(2) If you edit mpdecision with ANY text editor, the file will be corrupted and the system ignores the file as if it was not there. At least it appears to ignore the whole file... I have no way to prove it doesn't open it and read only part of it (or even read some of it wrong). Performance/batt is as above in (1).

(3) If you use the mpdecision file posted by Lrod a few pages back, that was edited in a text editor and only has the "userspace" --> "ondemand" change in the file. With that mpdecision file in place, I see no change whatsoever. The second CPU is offline when you check with System Tuner and benchmarks are identical to the original mpdecision file. I see no change in snappiness or battery life so at least with this ROM, it's my conclusion that properly changing "userspace" to "ondemand" in the mpdecision file is a useless change. Maybe it works differently with other ROM's/kernels.

Mike