[Sony Xperia P, U, Sola, Go] taboo5200:
This post is intended for only

rooted

users of Xperia go/P/U/sola phones that are currently running the

stock

firmware build 6.2.A.0.400 / Jelly Bean (or in the case of U/sola, the ported equivalent), and only users who are familiar with the

terminal

. If you satisfy the above criteria, read on.

Hi all, I've just discovered that disabling the second core of my Xperia go's CPU actually improves overall UI responsiveness in JB rather than the contrary, despite logic dictating otherwise. In fact, it's so smooth now that I can safely say it directly rivals GB's smoothness and response times (and this is from a long term GB user who just recently made the jump to JB, too).

I'm making this thread because I'd like to see if others will experience similar effects from disabling the second CPU core of their NovaThor U8500 SoCs.

Disclaimer: I am not responsible for anything in the unlikely event that you - somehow - break your phone from making this small tweak. Just saying. You should be fine if you follow the instructions, though.

You have to be running on

battery power

to be able to spot any difference since the UI's sluggishness isn't as noticable when connected to a power source. Oh, and leave your governor / clock speed settings at stock (i.e. interactive governor, 200 MHz min, 1000 MHz max) for a fairer comparison.

Open up a terminal window, then enter Superuser / root mode and enter the following command:

echo [B]0[/B] > /sys/devices/system/cpu/cpu[B]1[/B]/online

(that's a ZERO immediately after echo and a ONE in /cpu/cpu1)

This should immediately take the second core offline, you can verify it with the following command (do consider first opening an additional new terminal window for this purpose):

cat /proc/kmsg

Look for something along the lines of:

<5>[35017.521636] CPU1: shutdown

Now, start testing the responsiveness of the UI, it should be extremely smooth in comparison to what it normally is. Skeptics, please do feel free to drop your jaws at this point, because I sure did when I first tried this. I noticed that the processor's speed seemed to ramp up and down much more aggressively with the second core disabled, but that could just be me seeing things.

To re-enable the secondary core again, use this command:

echo [B]1[/B] > /sys/devices/system/cpu/cpu[B]1[/B]/online

(that's a ONE immediately after echo and a ONE in /cpu/cpu1)

You can verify that the core is enabled in the dmesg logs (remember the earlier cat /proc/kmsg command?):

<4>[35155.743408] CPU1: Booted secondary processor
<6>[35155.745011] Switched to NOHz mode on CPU #1

At this point, you're likely to see the sluggishness make a return.

This should be fairly obvious, but don't go doing "smart" (that was sarcasm, in case you missed it the first time) stuff like disabling the first core (or even both) because you'd clearly be asking for trouble.

I suspect that the presence of the second core is preventing the governor from ramping up the processor speed on battery power, leading to the sluggish UI response. It has been noted before that a pair of cores running at a lower clock speed can potentially be more power efficient than a single core running at a higher clock speed, so I'm not too sure how this would affect the phone's battery life. I haven't yet noticed any negative impacts of the change on battery life - if anything, battery life appears to be improved, but I'd like more people to test this out (preferably those on P, U and sola phones).