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Re: Who wants to build a mips64 and/or mips64el n32 port?

On 02/02/2012 02:42 PM, Aurelien Jarno wrote:
On Wed, Feb 01, 2012 at 03:56:33PM -0800, David Daney wrote:


We (Cavium, Inc.) are interested in working with one or more people
to create a MIPS 64 port of Debian.  As part of the effort, we can
make available one or more fairly high end machines.  These would be
cn5650 (12 CPU SMP) based, or similar, with 4GB of RAM and a large
SATA disk.

See: http://cavium.com/OCTEON-Plus_CN56XX.html

These are running unmodified Linux 3.2 kernels with mips/Squeeze
installed and at first would be big-endian only.

We can also run little-endian in the future, but we are interested
in attacking the big-endian problem first.

I think Debian would be interested in having a 64-bit MIPS port, but the
main problem is to have enough people interested and providing manpower.
The current mips and mipsel ports are not in a very good state, and are
already lacking manpower to fix the existing issues. That's why this
part is important, and it would be difficult to convince the release
team and the community in general to add a 3rd mips(el) port if the
already existing ones are not well maintained.

Although nothing can be guaranteed, I think there might be more interest in fixing problems in a port if the port addressed our needs. If you look at the types of MIPS machines out there where running a full distribution makes sense, there are many 64-bit systems. Old SGI gear off of e-bay, Cavium, Loongson, etc.

About the n32 port, I have to say I am not sure it's a good idea to go
for 32-bit nowadays. As far as I know n32 is still limited to a 2GB
memory space, and this already causes some issues in Debian. More and
more code reaches this limit (including GCC), issuing the now famous
"Virtual memory space exhausted". IMHO architectures with a 2GB memory
space will have a very limited life in Debian, that's why for example
the s390 port is being replaced by the s390x port. Architecture with 4GB
memory space can probably live a bit longer though.

Right, I have several thoughts on this:

o The kernel was recently changed to allow all of the 2GB to be used instead of about only 2/3 of it, so with a recent kernel things would be a little better.

o I do native n32 builds of GCC on an almost weekly basis (all languages except ada), and have never seen exhaustion of VM space.

o Intel has just come out with a new LP32 ABI on linux (similar to n32) to address performance issues with the x86_64 ABI. To me this validates the idea that we want most things running as n32.

So if a new MIPS port is created, I really advise to create a full
64-bit port.

I would like that too, but really as something that could be mixed and matched in a single instalation. But it would be more work to do both n64 and n32.

David Daney

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