Why I stopped using JIT - Droid Eris General

So I'd been using JIT on my Evil Eris ROM (and I'd used it with a few others) and I was getting scores of 5.1~ mflops. Here are some things I noticed.
While I had first enabled JIT it was glitch free. I can safely say at this point that any "speed increase" I'd noticed was likely placebo or at least admissible.
JIT is amazing, but it's amazing for Froyo. The way a JIT compiler works is that it precompiles information into code that is more easily read, causing slight lag to begin and increasing overall performance. The thing they had to do with froyo is optimize just about everything to stop the lag and to make JIT worthwhile.
The other reason is that despite removing sense and eventually using the Universal JIT and basically doing everything to make it stable JIT began to show problems. It was absolutely stable for a very long time but if I left my phone on for a few days or I started installing new programs/ a new launcher it would get glitchy and laggy. This likely goes back to what I said about JIT really being much better for Froyo. It came to the point that I felt slower than before I rooted.
Now that I'm not on JIT I can also overclock higher. Before I was limited to 768mhz and if I went over it was an instant crash. Now with JIT removed I'm up to 787, I can do 806 but it only lasts a few minutes before it freezes up but it's proof to the concept that I can overclock much higher. I get consistently 3.4~ mflops.
I do realize that I while on JIT I got a large increase in mflops but in my experience I am performing better without it. I think that when Froyo ROM's come out JIT will be much better implemented.
tl;dr: JIT ended up causing lag, I can overclock higher without it, I'm just as fast/faster without it.
note: For something like a game JIT may help you much more than just scrolling around since the game will be precompiled and then run more smoothly but in my experience (with Zenonia mostly) there was no improvement and occasionally I would in fact lag more.
Just thought I should say this to everyone.

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Kind a sounds like steroids, ya you get muscle and look cool but there are side effects

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Yeah and JIT was made for Froyo, not for the other ones. Froyo was heavily optimized, they spent a ton of time just making everything work as well as possible so that the JIT wouldn't actually be detrimental. So while JIT does increase MFLOPS and performance it can cause a lot of bugs and slow downs because it's trying to compile information that isn't optimized for it.

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Hm. I think I'll try disabling JIT for a while too. I might prefer the quicker load time over any supposed increase in performance. I haven't had much buggy behavior, but I have had some restarts and wonder if they're caused by JIT or just overclocking in general.

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I've found overclocking surprisingly stable without JIT. It's incredible that I can overclock to 806mhz now with glitches and 787 is absolutely stable...
Looking back I realize now that JIT had slowly degraded, I started off overclocking without it to 787 and as I turned it on it began to get very glitchy with 787, eventually freezing immediately with it. I wouldn't be surprised if the restarts you're having are due to JIT in combination with overclocking.

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good post +1.
the devs don't say anything about this in their threads, thats if they even know it or have experienced it themselves so i'm not blaming anyone.
good to know so i can at least eval it for myself. thanks.

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I think JIT might have been interfering with my Swype. Maybe it's doing too much "just in time" compiling and not enough "ahead of time" compiling. But anyway, yesterday I switched back and forth several times between using JIT and not using JIT, but didn't change anything else, and I definitely noticed that Swype was more responsive without JIT. With JIT enabled, I kept having to retype things because my tracing path would skip over parts; it was choppy. Without JIT it's smooth as silk and therefore accurate again.

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I think a lot of the problem is that apps also aren't made to use JIT yet, all of the developers made apps for non-JIT phones first... you see a LOT of problems in phones that have background apps (setcpu, autokillers, etc) when they have JIT enabled. I think anyone who read up on JIT when it was announced will see mentions of the google dev's saying "We really really streamlined the phone to make use of the JIT".... obviously they're remarking that JIT without streamlining and "light" OS is a bit of a waste. JIT on my Froyo ROM (CM6) is very much more stable. If anyone's interested I did some benchmarks for JIT here:
http://forum.xda-developers.com/showthread.php?t=726038

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Found this in the Hero forums, and it obviously applies to the Eris as well:
illogic6 said:
http://forum.cyanogenmod.com/topic/880-jit-wont-make-your-phone-super-fast/page__p__7910?#entry7910
Notice this portion of the post: "CPU intensive tasks get faster, but at the cost of RAM."
The way Darchstar explains it is that our phones cannot sacrifice that RAM once our phones have been bogged down with installed apps. He doesn't plan to include JIT by default when CM 6 goes final for HeroC and that's why.
Click to expand...
Click to collapse

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Yes well you can decrease or increase the amount of RAM that JIT will use (heap size) and increase stability or decrease it. I understand why it's default off, it makes sense especially since a lot of programs aren't made to use it *cough pandora cough*

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I'm running Cyanogenmod 6 froyo, did you test the effects of turning on and off JIT on this ROM?

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Yes, like I said JIT was literally made for Froyo ROMs, and you can quite clearly see that when you hear the devs who created it talk about it in google conferences and such, they had to do a lot to get JIT to work well without creating huge slowdown. Compilers are almost ALWAYS a bad idea because of their nature and because if information isn't made for the compiler it ends up doing more harm than good.
Froyo is streamlined to work with JIT without causing slowdown so I would highly recommend using the JIT compiler with Froyo.

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Hungry Man said:
Yes, like I said JIT was literally made for Froyo ROMs, and you can quite clearly see that when you hear the devs who created it talk about it in google conferences and such, they had to do a lot to get JIT to work well without creating huge slowdown. Compilers are almost ALWAYS a bad idea because of their nature and because if information isn't made for the compiler it ends up doing more harm than good.
Froyo is streamlined to work with JIT without causing slowdown so I would highly recommend using the JIT compiler with Froyo.
Click to expand...
Click to collapse
What about the Compcahe? Idk what it even does ahah

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I turned JIT and surface dithering off. Phone runs smooth and no force closes.

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surgeon0214 said:
What about the Compcahe? Idk what it even does ahah
Click to expand...
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Compcache can speed some things up. I enabled it on a SenseUI ROM a while ago and had TERRIBLE, crashing results until I turned it off, at random.
I can confirm that JIT's make Swype crash sometimes. I can do a 100 fast-swype word experiment (which, I do a lot of 'texting', so this experiment happens every day), on days I have JIT on, Swype randomly disappears. (it is set to restart itself after 5.0 seconds, so don't worry). With JIT off, it only does its normal random crashing (when I accidentally hit the Swype key while it's thinking of what words I just swyped, for example -- just the known crash bugs).
JIT day was yesterday, for example (I'm experimenting with JITs because of this thread) - and Swype crashed more than 10 times (I stopped counting by the time I was at the bar for two hours, -- don't drink and swype!)
Non-JIT day was today, and Swype has not crashed 1 time (despite writing a few very long emails in a passenger seat and some serious texting).
Monday is a JIT day, and I'm pretty confident based on my findings, that these have a huge impact on Swype.
I'm just using SenseUI for the weekend (for reliability/etc, because I'm 'On Call' for work), but if my findings prove my theory WRONG, I'll edit this post and note that.
But in general, yes, I agree, JITs mess with Swype. Not to a point of usability, but to a point that, the late person might think Swype is unreliable (unknowingly).

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Compcache is your processor compressing the information that is stored in your RAM to increase the total amount of RAM that you can use per program. This can increase performance by letting your programs use more RAM but it can also decrease performance by increasing the time that the CPU has to work on compression. For the Eris I don't suggest Compcache unless you're overclocking to at least 710mhz and if you're on a Froyo ROM I don't suggest it at all since you should have plenty of RAM already.
What VM Heap Size are you using pkopalek? Smaller heap sizes are more unstable, you may find swype is more stable at 24m if you're at 12 or 16. 24m is the point where sense becomes stable (sorta) with JIT.