Anders Logg wrote:
> On Wed, Aug 20, 2008 at 06:17:30PM +0200, Niclas Jansson wrote:
>
>>>> Stage 2 seems to involve a lot of communication, with small messages.
>>>> I think it would be more efficient if the stage were reorganized such
>>>> that all messages could be exchanged "at once", in a couple of larger
>>>> messages.
>>> That would be nice. I'm very open to suggestions.
>> If understand the {T, S, F} overlap correctly, a facet could be globally
>> identified by the value of F(facet).
>
> No, F(facet) would be the local number of the facet in subdomain S(facet).
>
>> If so, one suggestion is to buffer N_i and F(facet) in 0...p-1 buffers
>> (one for each processor) and exchange these during stage 2.
>>
>> -- stage 1
>>
>> for each facet f \in T
>> j = S_i(f)
>> if j > i
>>
>> -- calculate dof N_i
>>
>> buffer[S_i(f)].add(N_i)
>> buffer[S_i(f)].add(F_i(f))
>> end
>> end
>>
>>
>> -- stage 2
>>
>> -- Exchange shared dofs with fancy MPI_Allgatherv or a lookalike
>> -- MPI_SendRecv loop.
>>
>> for j = 1 to j = (num processors - 1)
>> src = (rank - j + num processors) % num processors
>> dest = (rank + j) % num processors
>>
>> MPI_SendRecv(dest, buffer[dest], src, recv_buffer)
>>
>> for i = 0 to sizeof(recv_buffer), i += 2
>> --update facet recv_buff(i+1) with dof value in recv_buff(i)
>> end
>>
>> end
>
> I didn't look at this in detail (yet). Is it still valid with the
> above interpretation of F(facet)?
>
> --
> Anders
>
Yes, I think so.
Niclas
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