Backdoorbobby
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2 Pis running in parallel?

Mon Nov 03, 2014 7:49 pm

I'm pretty new to the computer world, but I have a lot of thing I would like to try to do. One thing I want to try is have two pis running in parallel to more smoothly emulate games, particularly gamecube which I have read is not the smoothest gameplay on retropi.

My question is, would it be possible to set up two pi's working together on the retropi operating system, and if so can anybody give me some tips?

thanks,
Bonby

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DougieLawson
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Re: 2 Pis running in parallel?

Mon Nov 03, 2014 7:55 pm

Sorry, it's not possible.

To use a loosely coupled cluster needs special programming and there's a whole bunch of overheads in running clustering that would swamp the diddy small slow processor and slow I/O subsystem on your RPis.
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Backdoorbobby
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Re: 2 Pis running in parallel?

Mon Nov 03, 2014 8:03 pm

Thats for that lightning fast reply. Do you know if there are any alternatives to the raspberry pi which could be compatible with retro pi and possibly be able to handle games the pi couldn't?

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DougieLawson
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Re: 2 Pis running in parallel?

Mon Nov 03, 2014 10:32 pm

No. Try running on a bog end Windows system.
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Nfarrow
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Re: 2 Pis running in parallel?

Sun Dec 28, 2014 11:28 am

It is very possible to cluster the Pis and use each resources on each but you would need to know how to use a clustering software called, "MPI http://www.mpich.org/" This software allows for multi-processing communication between computers.

Follow these instruction to get MPI working on the PIs
http://www.tinkernut.com/2014/04/27/mak ... -computer/

Now since you have, "MPI for Python" installed you need to find a Python emulator. Maybe try shedskin for a NES emu.
https://code.google.com/p/shedskin/downloads/list
Last edited by Nfarrow on Wed Dec 31, 2014 3:10 am, edited 1 time in total.
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ghans
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Re: 2 Pis running in parallel?

Sun Dec 28, 2014 12:27 pm

This is simply not possible , all emulators would have to
be rewritten as cluster software for this to work.
Not to forget that the Pi is a lousy cluster machine from a
price/performance ratio and technical standpoint , since the
overheads are immense (and *will* negate any
theohetic improvements of a 2-node cluster).

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Jessie
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Re: 2 Pis running in parallel?

Mon Dec 29, 2014 5:31 am

The software would require a rewrite and there would be a latency hit. This question gets asked every now and then and I think there isn't a reasonable solution. Even if someone managed to make this happen scaling would be far less than double. Syncing two pi over ehernet or usb would not work great. The best case may buy an extra 5 to 10% and that hardly makes the hastle of all the work that would be required.

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mahjongg
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Re: 2 Pis running in parallel?

Mon Dec 29, 2014 12:53 pm

The only way this could work to some degree if you could give a master and one or multiple slave PI's clearly separated tasks that would require minimal interaction. One such separations that comes to mind is to let one PI run "main PI" the processor emulation, one PI the graphics subsystem, and another PI the sound system.

This still would require an extensive emulator re-write, but IMHO it could be done.

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Jessie
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Re: 2 Pis running in parallel?

Tue Dec 30, 2014 7:42 am

There are generally 4 areas that can be paralleled in an emulator (yes a tad simplified). Cpu, gpu, sound, input output.

Two of them have tight coupling... the most demanding of the two. Sure due to the pi's in order arm processor not slicing that time up would help. But many of these emulators don't offload much to the gpu so there is still room for improvement. But that is why I think multi-pi emulation would have minimal pay out. The easiest implementation would be Pi 1 cpu+gpu work, Pi 2 sound and all else. The sound and io is just not enough to do all the work for an emulator rewrite.

I would love to see someone prove me wrong though.

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