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I have samsung galaxy nexus with CM-11 nightly 07-04-2014.

About twice a month I update my version to the latest nightly build and it was pretty good for a while. Unfortunately last time ( for a couple of weeks ) there were two updates which really slowed down my device. Every app starts now up to 10 seconds. Even when I get a phone call sometimes the phone is not fast enough to display me an answer call button. And the network became slow as hell. CM update download over wifi will take up to several hours, while before it was about 5 minutes. However wifi in local network works a bit faster. gprs inet also works very slow. 100K pdf download takes up to 5 minutes, while it was up to 10 seconds before.

I tried to downgrade to the last stable version I had ( it looks like any before 03-25 ), but without success. Important note: I did not perform the whole wipe during downgrade. I only formatted /system and /cache. I also tried to install other nightly builds with the same result.

There is nothing suspicious in dmesg or logcat. Sometimes in dmesg I can see messages about killing some users apps but it seems normal to me.

How to find the root of such slowdown?

And I'm not sure if the whole wipe will help me, as I'd like to save app data and restore it after wipe.

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As far as I now Android device slowdown can occur for several reasons:

  1. Very low amount of free RAM. Check under Settings>Apps>Running how much free RAM you have If your free RAM is too low (70-150MB or less) it's probably the cause so check which app/apps, if it's not an app maybe it's a bug in the ROM. (see 3)
  2. Low free space on internal storage. (check under Setting>Storage) If the free space is too low (~2GB or less), try free up some space and check if that helps
  3. Kernel bug/misconfiguration. Try to check your CPU usage stats, clock speed, governor, number of active cores etc... (If you havn't flashed a custom kernel and never changed the governor/clock speed or other performance settings it's probably not the problem)
  4. ROM bug You can try perform a nandroid backup, then reinstall the rom after full wipe and see how it performs, if it's still slow, try clean install of the version that previously worked fine (only if you know what you doing!)
  5. Bug in one of the user apps. If your CPU/RAM usage is too high for no reason maybe one of your apps eating it. I recommend you to try OSMonitor or any similar app to find which app eating your CPU/RAM.
  6. (Lack of TRIM, TRIM does exist in Android 4.3 and up so it's not the problem)
  7. (In some rare cases bad sdcard can cause such problem but it's not the problem too since Galaxy Nexus doesn't have card slot)
  • There are definitely a lot of free RAM (>30%) and about 5Gb of free space. However for point 3-5 it may be an option. I will try to check it. Thanks for the links. – rush Apr 11 '14 at 5:17
  • @rush about point 3: If you use stock CM Kernel (eg. never flashed custom kernel on this ROM) you can see current governor and clock speed under settings>performance, but be carefull there – 2rgman Apr 11 '14 at 5:25
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Cyanogenmod nightly builds are unstable and will show bugs like this from time to time. They're really not suitable for everyday use, and sooner or later one of these bugs might wipe all your data, or turn your phone into a pocket heater by running the CPU at 100% continuously.

To avoid the problem you've seen, either update (downdate) to a nightly that doesn't have this problem, or switch to something more stable such as a beta build.

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I would suggest a full wipe to determine if it's a hardware or software issue. You can save data from your apps through a utility like Titanium Backup (be sure to copy the backup files out of your device after you have performed the backup tasks).

Just to be sure, did you change the runtime to ART or are you still on Dalvik? ART is extremely unstable on CyanogenMod builds since 31 Mar 2014

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