Hey everyone,
So, I was experiencing significant lag as we all do from time to time, and decided I was going to get to the bottom of it.
After tracing and debugging for hours, I discovered the source of 90% of Android's lag. In a word, entropy (or lack thereof).
Google's JVM, like Sun's, reads from /dev/random. For all random data. Yes, the /dev/random that uses a very limited entropy pool.
Random data is used for all kinds of stuff.. UUID generation, session keys, SSL.. when we run out of entropy, the process blocks. That manifests itself as lag. The process cannot continue until the kernel generates more high quality random data.
So, I cross-compiled rngd, and used it to feed /dev/urandom into /dev/random at 1 second intervals.
Result? I have never used an Android device this fast.
It is literally five times faster in many cases. Chrome, maps, and other heavy applications load in about 1/2 a second, and map tiles populate as fast as I can scroll. Task switching is instantaneous. You know how sometimes when you hit the home button, it takes 5-10 seconds for the home screen to repopulate? Yeah. Blocking on read of /dev/random. Problem solved. But don't take my word for it .. give it a shot!
Update!
I've built a very simple Android app that bundles the binary, and starts/stops the service (on boot if selected). I'll be adding more instrumentation, but for now, give it a shot! This APK does not modify /system in any way, so should be perfectly safe.
This is my first userspace Android app, so bear with me!
Note that this APK is actually compatible with all Android versions, and all (armel) devices. It's not at all specific to the Captivate Glide.
Caveats
There is a (theoretical) security risk, in that seeding /dev/random with /dev/urandom decreases the quality of the random data. In practice, the odds of this being cryptographically exploited are far lower than the odds of someone attacking the OS itself (a much simpler challenge).
This may adversely affect battery life, since it wakes every second. It does not hold a wakelock, so it shouldn't have a big impact, but let me know if you think it's causing problems. I can add a blocking read to the code so that it only executes while the screen is on. On the other hand, many of us attribute lag to lacking CPU power. Since this hack eliminates almost all lag, there is less of a need to overclock, potentially reducing battery consumption.
If you try it, let me know how it goes.
ROM builders - feel free to integrate this into your ROMs (either the .apk / application, or just the rngd binary called from init.d)!
If anyone's interested, I've launched a paid app on the Play store for non-xda users. As I add features I'll post the new versions here as a thanks to you guys (and xda community at large for being such a great resource). But if anyone's interested in the market's auto-update feature, just thought I'd mention it.
