Porting 3.8-rc4-nohz3 to ARM (PandaBoard)

Mats Liljegren [off-list ref] writes:

Frederic Weisbecker wrote:

quoted

2013/2/4 Mats Liljegren [off-list ref]:

quoted

Hi Frederic,

(Sorry for the re-post, I spelled the mailing list wrong...)

I want to port dynticks patches 3.8-rc4-nohz3 to ARM architecture,
and try it out on the PandaBoard. Initially this is for evaluating
it, but if it looks promising I'd like to upstream this.

As far as I can see the first thing to do is to implement virtual
time accounting. After an initial look at the patches done for
ia64, it doesn't look too difficult.

No that part is handled by the core code. But you need to implement
the context tracking arch backend.
Here is what Li Zhong did to port it on Powerpc for example:
https://lkml.org/lkml/2013/2/1/216

quoted

Are there any caveats I should be aware of?

The generic cputime accounting only works on 64 bits archs. We'll need
to do some safe accessors to read the kernel_stat. In the meantime you
can do home tests by removing the CONFIG_64BIT dependency. This
shouldn't be dangerous

quoted

Has anyone else started any work in this area that I could co-operate with?

Yeah two people have been working on this. But it was several month
ago and I haven't hear from them since then. I'm adding Geoff in Cc. I
can't retrieve the other guy who has worked on it too.

Could the other guy be Kevin Hillman? 

Yup, that's him (though my last name has only one 'l' ;)

The name has been mentioned to me but I don't have his e-mail address.

Now you do. :)

After some time away, I'm back to working on getting adaptive nohz
working on ARM, but things have changed quite a bit since I last worked
on it.  Things actually look a bit simpler now with the new
context_tracking layer, but that needs a little work for ARM which I'm
now looking into.

However, just to get things compiling needs a little work too.  I've
setup a work-in-progress branch which you can start from to at least get
things compiling[1].

I noticed you already ran accross the 64-bit division problem.  I've
proposed a patch for that[2] which is included in my branch along with a
few other things.

Hope that helps,

Kevin

[1] git://git.kernel.org/pub/scm/linux/kernel/git/khilman/linux.git wip/3.8-rc6-nohz4-arm
[2] http://marc.info/?l=linux-kernel&m=136087139214252&w=2