Gentoo on Raspberry Pi 2

el_Salmon · Posted: Mon Feb 09, 2015 8:08 am Post subject: Gentoo on Raspberry Pi 2

Hi,

I'm ordering a Raspberry Pi 2 to replace my old RPi 1, that runs Raspbian (Debian) currently. I'm thinking to begin to use Gentoo Linux but I'm not sure if the new model be able to compile ebuilds itself without distcc. I'm suppose it does, because is a Quad-core 900 MHz with 1 GB DDR2 RAM. What's your experience or technical opinion?
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Roman_Gruber · Posted: Mon Feb 09, 2015 8:18 am Post subject: Re: Gentoo on Raspberry Pi 2

Nope. AFAIK its arm, like my smartphone and that architecture has not much calc power.

snkmoorthy · Guru Joined: 19 Nov 2002 Posts: 376

http://wiki.gentoo.org/wiki/Raspberry_Pi

use crossdev on your powerful machine and compile for armv6[7] to your hearts content. Native compilations will be slow.

Leio · Developer Joined: 27 Feb 2003 Posts: 494 Location: Estonia

BogoMIPS is NOT usable for performance comparison between different CPUs. Especially not with ARM vs not ARM - http://en.wikipedia.org/wiki/BogoMips#Timer-based_delays

With RPi2 now being quad-core, native compilation isn't that slow; and together with --jobs=n or something, to battle slow single core configure runs, it shouldn't be all that bad. Of course at least distcc is hugely desirable still.

I didn't find any RPi2 specific material in our wiki page yet, so keep that in mind (CFLAGS, etc). But most other things are equal, including graphics stuff.
I'm setting up a full graphical system on RPi2 with Gentoo now, so happy to share notes, mostly via IRC. #gentoo-embedded or #rpi-gentoo channel or something.

Roman_Gruber · Posted: Tue Feb 10, 2015 7:39 pm Post subject:

I read about today taht the cpu gets full utilization when playing fullhd videos. i do not trust much about golem.de knowledge base at all.

I am interested in user expierence here.

The hardware could be fun for some small projects though I wonder if I can find really a use case for it

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

I tried Gentoo on a model b+ for awhile. Never got a working kernel, I robbed the one from Raspbian and used that mostly.

A kernel compile on a B+ is 10+ hours unless something went wrong. If you can avoid doing a clean, subsequent compiles are quicker. First time I've ever spent less time configuring the kernel than compiling it on Gentoo. Back in the pentium days I could, because the kernel was a lot simpler and CPUs slower than the pi.

I also had tried to set up Gentoo for distcc but never got it to work from the pi.

You're using armv7 where I was using armv6, so that might make a difference by itself.

My opinion is that if you're doing this for fun and have lots of time and patience, then it might be worthwhile. If you actually want to use the pi for a project and don't need an extremely customized install then it's probably better to trim down/modify some other distro.

Leio · Developer Joined: 27 Feb 2003 Posts: 494 Location: Estonia

CPU utilization ought to be in the 20% area of one core for 720p/1080p playback. At least so it was with the weaker model, and all the video bits are still the same, just with different/more memory.
If it's full utilization, they are doing something wrong and aren't using acceleration via OpenMAX properly.
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Leio · Developer Joined: 27 Feb 2003 Posts: 494 Location: Estonia

Setting up distcc is trivial with portage on rpi and crossdev on the helper machine.
Just did a toolchain for rpi2 to my desktop today

keet · Guru Joined: 09 Sep 2008 Posts: 573

I just got my Raspberry Pi 2. I'm thinking of using it as a file server. The only problem is that the storage would need to be encrypted, and my Raspberry Pi 1 was much too slow for this (3MB/s). Does anyone here know how well the 2 performs in this respect? I hope to start installing Gentoo on it soon.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

100 mbps nic should tell you everything you need to know about a pi as a file server.

keet · Guru Joined: 09 Sep 2008 Posts: 573

I have mine working so far. I downloaded a stage 3, but took the boot files from a Raspbian installation. After that and other basic configuration, I set up distcc, ran 'emerge -e system', and installed a few world packages.

I got the Raspberry Pi 2 kernel sources from Github and built them within an hour or so, and rebooted successfully.

Udev failed to build, so I am curious about that, but I'm not worried about it.

Another odd thing that I noticed is that only about 750MB of R.A.M. are available. I set gpu_mem=16, so that is probably not the problem. Considering that it has four cores, and only 1GB of R.A.M., it would be nice to have more available. A potential fix is at http://www.raspberrypi.org/forums/viewtopic.php?f=56&t=98997&start=25, so I will try that when I have time.

Leio · Developer Joined: 27 Feb 2003 Posts: 494 Location: Estonia

olek · Apprentice Joined: 22 Oct 2011 Posts: 173

I'm using the original model B and even compile everything right on it with an attached hard drive.
it's a headless server and I also like to choose less boated software on all of my machines. it works fine.
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keet · Guru Joined: 09 Sep 2008 Posts: 573

Choosing VMSPLIT_2G fixed the memory problem; I now have about 975MB. Thank you for the tip.

Now I'm working on building media-tv/kodi-14.1. I a'm not sure whether I will end up using this, but I want to see whether it works. Of course, it's in ~x86 and ~amd64, but not marked for arm at all, but I'll try it.

Yamakuzure · Posted: Fri Feb 27, 2015 3:55 pm Post subject:

Yamakuzure · Posted: Fri Feb 27, 2015 6:56 pm Post subject:

Solved it myself.

As you can see above, I am using gcc-4.9.2. The problem is, that this does not set __ARM_ARCH (ARM support was dropped?) and in the glibc build dir one can find in sysdeps/arm/sysdep.h:

UncleVan · n00b Joined: 08 Feb 2011 Posts: 72

Hi Leio,

Now, this wold be my second Gentoo ARM clone, since I succesfully build a fully functional distro for Raspberry Pi model B: cross(dev) toolchain, kernel from source, distcc/qemu user emu etc - details on request - but I have a pretty basic question about the cross-compiler:

How you came across this tuple:

cwr · Veteran Joined: 17 Dec 2005 Posts: 1969

A while back I built a Gentoo system for a BeagleBone Black which had the root filesystem on NFS.
Cross-compiling the kernel wasn't a problem, and nor was most of the other cross-compiling
I did. I found an ARM Stage 3 somwhere, and built relatively few packages; some stuff (eg. Python)
had to be build natively.

Will

Leio · Developer Joined: 27 Feb 2003 Posts: 494 Location: Estonia

UncleVan · n00b Joined: 08 Feb 2011 Posts: 72

@Leio : Thanks - nevertheless it's a fuzzy area ;-)

@cwr:
Simply cross compiling on the host - "i686-pc-linux-gnu" - didn't work well for me either, or is simply too complicated. You can run builds on the target - Raspberry Pi for me - with cross-distcc on some bigger machine; but is still very slow, because all autoconf checks and unpack/install stuff are still local.

Best way I found is with qemu user emulation + chroot into the target file system; could be directly on the SD card too. You'd need binformat (module binfmt_misc) enabled & set up - in the "local" services for example.
Everything is very well documented by Gentoo or Sysresccd.

This waS THE ONLY WAY FOR ME TO RECOMPILE THE GCC ITSELF TO 4.7.3

Funniest thing is if you still could use cross-distcc on the same machine to utilize other cores, gotta try this out.

PS:
Dont know whether applicable for BB though...

PPS:
don't forget to comment out the line in the /etc/ld.so.preload if you are emulating into the original raspbian, or qemu will core-dump

el_Salmon · Posted: Wed Mar 04, 2015 4:31 pm Post subject:

f.kater · Guru Joined: 23 May 2002 Posts: 342 Location: Berlin

Just for those thinking about cross compiling, qemu or direct compilation on
the RPI:

I've tried all the three ways, but finally found that compiling on the RPI is
absolutely ok for everything that might be necessary on that box (samba,
gnumeric, ...), compared to the whole configuration overhead you have with
maintaining gcc/arm cross-compilers, the whole qemu image, dependant arm
libraries etc.

Just compile on the RPI -- I am using the old A model (with systemd
and paludis/cave instead of emerge).

About the kernel: Get the rpi kernel sources via github. Note: Since the
developers are working on new versions constantly, make sure you grab all the
required commits on top of the usual kernel tag (this might require to compare
two or three version tags to understand what is required extra stuff). And
then just try the "simple" kernel config example given in the kernel sources as
a start. I only had to add the HID driver for my cherry keyboard later on.

The resulting kernel is quite small, compilation takes way less than 10+ hours
(see postings above). Also, you might want to avoid kernel modules totally,
so you can exchange kernel images easily.

UncleVan · n00b Joined: 08 Feb 2011 Posts: 72

Sorry Kater, cant confirm nor recommend: It is much better - and easier in long terms - to spend, say, 6 hours to set up arm cross-compiler + distcc and user-qemu ONCE and them use it anytime anywhere, then to wait days and weeks for some native build. It can not recompile gcc itself (and most other complex stuff) just bec. lack of memory - as far as Raspberry 1 is concerned. I still dont have model 2, but curious about it's gcc performance...

Last evening build the Raspperry kernel 3.18.8 from git:

Leio · Developer Joined: 27 Feb 2003 Posts: 494 Location: Estonia

ShiroiKuma · n00b Joined: 09 Nov 2012 Posts: 40 Location: Japan

Just wondering, has anyone got "crossdev -S -v -t armv6j-hardfloat-linux-gnueabi" to work on the Pi2 yet?

Thanks to this thread my Pi2 is running nicely with Gentoo, but thinking... maybe I could use the Pi2 to assist with compiles (distcc) from the Pi1 still laying around.

Everytime I try crossdev I'm ending up with a "the selected processes does not support thumb" error. Just trying one last time with "CLFLAGS="-marm" crossdev -S -v -t armv6j-hardfloat-linux-gnueabi" to see if that helps but I'm not holding hope. It's only the final glibc stage that's failing.