last few days, the Linux world has paid quite a lot of attention to this kernel patch, written by Mike Galbraith.
Its purpose is to make your desktop more responsive by grouping your tasks so that they have a better chance at getting their fair share of CPU time when some other task, notably a CPU hog, is running in the background. Lennart Poettering then offered his own solution, which requires no tweak of the kernel itself.
While Mike’s approach adds the concept of tty grouping to cgroup, Lennart’s one consists of grouping every task you launch under your own bash shell. The latter take actually offers better granularity.
It appears that this tweak just works. Hurray, then.
On Reddit, the question was asked: Does any one know if this linked linux speed patch will work on an ( linux based) android phone?
I’ve seen several replies that were quite off the mark so I added my own (I
like being wrong too!)
Allow me to expand on it a little here:
Out of curiosity, I did a line-by-line comparison of the scheduler code
between three kernels: Linux stock 184.108.40.206, Android snapshot branch and HTC
Incredible MR3 2.6.32.
Well, they are all different. But the question is: how different? In this case, not different enough to be seen as “different schedulers.”
Overall, the three branches use the fair scheduler. With these differences:
Unsurprisingly, the Android code cares about task freezing.
On the Android side, the real-time portion does not let you add a task to the head of the queue
It seems more concerned with proper IRQ handling
The Incredible code aligns its timing on the clock rather than raw CPU time, again – I suppose – out of care for overall sync., including IRQ timing (It also pushes the logic a bit further by making sure that it uses the high-res timer)
All tasks’ iowait time is included in init ’s own iowait time. My guess is for statistics purpose; possibly including battery life.
Tasks enqueuing is simplified to ignore the “migrate” flag. However, load balancing is implemented and CPUs can be found not eligible for process migration. If they are, the same algorithm is used as in the stock kernel.
When attaching a task, Android does not immediately check for ownership. It does, however, make up for this by testing that the process has the CAP_SYS_ADMIN Posix capability.
Oh, how exciting.
So, what does this mean for Android? Can we just tweak a phone as we would a
Unfortunately, the answer is no.
Even though cgroups are alive and well in our phones, you do not log in on different ttys (best concise-yet-accurate comment winner), which means that the kernel patch would not really help. And we do not have a bash shell that we could rely on to apply Lennart’s tweak.
OK, allow me to add a caveat : we may be able to group the applications you get from the market on one side and the phone’s system applications on the other. This would be a different tweak but in the same spirit.
This would not do anything to prevent market application “A” from starving market application “B”, though.
As far as I can tell, Android does not see strong enough a difference between activities and services for it to be useful either.
Need more cowbells!
Note, too, that while Android’s code is ready to handle load balancing, this
would not helps us much. Let’s have a look a the three current top sellers:
Ouch. Not much to balance against. This should change when the next generation of SnapDragon is released as it should have multiple cores.