[Jolla Tablet] High standby CPU when not charging, becomes unresponsive

asked 2016-04-11 20:44:57 +0300

Andy Branson
4998 ●64 ●98 ●87

 

updated 2016-05-16 19:04:31 +0300

Edit: I've noticed that my tablet hasn't locked up for several weeks. I'd been keeping it plugged in, but have recently started leaving it unplugged and it seems fine. The cpu usage is still reported as high by top, system monitor and lighthouse, but that may be a problem with reporting the CPU suspend time as usage.

Often after using my tablet I noticed that it would be unresponsive after sitting on standby for a while. I assumed the battery had drained, but after plugging it into a suitable charger and managing to get it to turn on again, the battery would be at 70% or so. After running the System Monitor app for a while, I noticed that these episodes came after a long period of high CPU usage (about 65-80%), which started when the tablet was in standby. It doesn't happen every time, and never when the tablet is charging afaik. System Monitor only told me that these were system processes, not user.

Today I looked a bit further into it, and tried to get something out of top. I can't be sure it's correct, because being connected over ssh stops the tablet suspending properly. I saw a succession of kworker processes take heavy CPU, then get replaced by another. I took some dumps with /proc/sysrq-trigger, but that didn't really give me anything consistent, so I managed to install perf (and less, which for some reason I needed to get from mer-tools). The report gave me the following as the top consumer, and I assume [bcm4330] is driver related. I don't have any debug symbols though, so it's all just numbers.

# Overhead          Command                     Shared Object
# ........  ...............  ................................  ...........................................
#
    86.33%          swapper  [bcm4330]                         [k] 0xffffffff820163a6
                    |
                    |--72.96%-- 0xffffffff8265cd72
                    |          0xffffffff8265cec9
                    |          0xffffffff8265d01e
                    |          0xffffffff8200b11e
                    |          0xffffffff820e2bee
                    |          0xffffffff828d7c5f
                    |          0xffffffff83220e8d
                    |          0xffffffff832205e5
                    |          0xffffffff832206ae
                    |
                    |--20.66%-- 0xffffffff8265cd79
                    |          0xffffffff8265cec9
                    |          0xffffffff8265d01e
                    |          0xffffffff8200b11e
                    |          0xffffffff820e2bee
                    |          0xffffffff828d7c5f
                    |          0xffffffff83220e8d
                    |          0xffffffff832205e5
                    |          0xffffffff832206ae
                    |
                    |--1.86%-- 0xffffffff8265cd70
                    |          0xffffffff8265cec9
                    |          0xffffffff8265d01e
                    |          0xffffffff8200b11e
                    |          0xffffffff820e2bee
                    |          0xffffffff828d7c5f
                    |          0xffffffff83220e8d
                    |          0xffffffff832205e5
                    |          0xffffffff832206ae
                    |
                    |--1.85%-- 0xffffffff8265cd7c
                    |          0xffffffff8265cec9
                    |          0xffffffff8265d01e
                    |          0xffffffff8200b11e
                    |          0xffffffff820e2bee
                    |          0xffffffff828d7c5f
                    |          0xffffffff83220e8d
                    |          0xffffffff832205e5
                    |          0xffffffff832206ae
                     --2.67%-- [...]