My phone has lately been really slow. When I turn on the screen, particularly if it has been off for a while, the phone is really sluggish. For example, it might take 30 seconds to respond to my input. Or if someone calls, it might not respond to my answer gesture until after the caller has already given up and hung up.
If I leave the screen on for several minutes (up to five), the phone will eventually start to respond more normally.
The CPU information in the developer options shows that the processor is pegged during all this slowness, and the process system_server is consuming almost all of that CPU capacity with other processes fighting for a little CPU time.
Also, this CPU activity is killing my battery. I'm only getting half the battery life I should be getting.
I recently lost root in an OTA upgrade; in re-rooting I had to do a wipe of the phone. Once I restored everything, the problem came back.
My phone is a Galaxy Nexus running Jelly Bean (4.1.2). I also experienced a similar issue with my previous phone, a Nexus One running MIUI and "ICS". I attributed that phone's slowness to its age, but now I think there must be something else going on.
What could be wrong, or how could I go about tracking down the problem?
This looks like it could be an issue with certain background services malfunctioning. Try observing the background services and disable some of them to see if you might hit the culprit. To do it in a way that is less hit and miss, there are several battery app in the market or you can use ICS native battery monitor to see if there are anything that are consuming more battery than it really should.
I've had a similar issue with my new mobile, Razr Maxx running ICS. It turned out to be an overzealous car HUD application that consumed CPU cycles even when not running. Uninstalling it solved the problem. What confused me initially was that Android OS was shown as the main battery drainer and not the app itself. Since you had the same issue with your previous phone, this suggests a misbehaving application that you have installed on both.
I would try turning off GPS and mobile data/Wi-fi and observe whether the battery continues to drain at a similar alarming rate. If it's the internet connection that triggers the problem, this is likely due to an ad-supported application unsuccessfully trying to phone home.
Another very common source of Galaxy Nexus slowdowns is quite a nasty hardware/firmware issue documented here: http://code.google.com/p/android/issues/detail?id=39154 .
This will probably affect you if you have less than 3 to 4Gb storage free. There are some workarounds but they involve root and thus possible warranty invalidation. I found that clearing out some storage and rebooting does help somewhat, but have not yet tried the workarounds.
Check the running services. You will know what is running unnecessarily. I closed these, and I could immediately see a change in speed.
This is driving me nuts. I have SeePU installed so that I can see a CPU graph on my Moto Droid. When I unlock the phone after being idle for a while, the CPU is pegged by android.process.acore and the phone is unusable for 15-45 seconds, which is an eternity when you are trying to answer the phone!
UPDATE: I un-installed most of my apps, and I seem to have licked the problem for now. I'm gonna try adding one app back a day until it gets stupid again. If I can find a particular app that causes this problem, I'll post it here
Are you over/underclocking your CPU at all and/or using profiles?
A lot of users will underclock their CPU when the phone is sleeping, which may save battery. However, if you underclock too much (125 MHz), the phone will lag like crazy when it wakes. It is recommended to never underclock further than 250 MHz.
Aside from that, I'm not really sure anything would cause this to happen and would need more information to help you diagnose.
Instead of doing that , just try with WatchDog app , which finds which App uses more of your memory or slow downs your Android Phone ..
Hope it helps you ..