Re: [microblaze-uclinux] uclinux / MicroBlaze SMP

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Steven, Alex,

Alex Gibson wrote:

> Stephen Craven wrote:
> 
>> Does anyone know the state of SMP on the MicroBlaze?
>>
>> What hardware modifications, other than a coherent cache, are needed?
>>
>> Many thanks!
>> Stephen Craven

I've recently booted a dual MicroBlaze/uClinux system.  However, this is
not SMP, it's just two independent Linux kernels running from a shared
memory.

The biggest technical gotchas with SMP will be cache issues.  We've
considered making a cache snoop unit that could be used to force
invalidations on other CPU caches, but since the caches are bulit into
microblaze it's not currently possible to do a hardware-only solution.

But, as Goran says, the returns from SMP diminish rapidly, shared memory
access will quickly become a bottleneck.  (Coherent) caches obviously
help, but you quickly run out of BRAM on the FPGA.

The nice thing about SMP is that since it's one virtual machine, your
software gets its parallelism for free (sort of).  However, scaleability
is poor.

> No idea but I still haven't got a reply on openmp / mpi with microblaze.

> Question was didt any one know of any open mp or mpi implementations for
> microblaze or ppc
> that work with/in the edk ?

I'm looking into MPICH2 for MicroBlaze / uClinux, for the project we are
doing with NASA.  If/when it reaches a fit state for release we will do
so, but you shouldn't expect anything before next year.

As for putting MPI functionality directly onto microblaze (without
uClinux), I'm not aware of any.  You may be able to leverage the MPICH
architecture, with its abstractions and layers, but it would still be a
big job.

Regards,

John


>

> 
> Alex
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-- 
Dr John Williams, Research Fellow,
Embedded Systems Group / Reconfigurable Computing
School of ITEE, The University of Queensland, Brisbane, Australia
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