dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 21/02/11 18:00, Johan Hake wrote:
> On Monday February 21 2011 08:18:18 Garth N. Wells wrote:
>> On 17/02/11 21:28, Johan Hake wrote:
>>> Hello!
>>>
>>> I have a not so large 3D mesh of some 50K vertices, generated from some
>>> geometry (not UnitCube).
>>>
>>> When I set
>>>
>>>   parameters.num_threads = 2
>>>
>>> and try to assemble I just get:
>>>   Coloring mesh.
>>>
>>> and then it seems it wont find a solution... I had to break it because it
>>> nearly hang the computer for some 5 min.
>>>
>>> Have anyone experience the same? Is there any way to controll the
>>> coloring?
>>
>> It's had minimal testing, so issues can be expected. Can you post your
>> solver? 50k vertices is not very big, so I would expect it to be pretty
>> fast.
> 
> Yes I would expect that too. I have used the coloring on other meshes with 
> success.
> 
> The mesh can be downloaded from here:
> 
>   <http://folk.uio.no/hake/trouble.xml.gz>
> 
> To reproduce the trouble just run:
> 
>   from dolfin import *
>   mesh = Mesh('trouble.xml.gz')
>   V = FunctionSpace(mesh, "CG", 1) 
>   assemble(Function(V)*dx)
>   parameters.num_threads = 2
>   assemble(Function(V)*dx)
> 
> The mesh has two distinct domains, but that shouldnto be causing the trouble, 
> as other I have successfully colored other such meshes. I guess it can be the 
> particular mesh that causes coloring to stall. It is generated using tetgen. 
> 

I don't think that I've tested multi-threaded assembly for functionals.

When we get around to implementing it, assembling functionals shouldn't
require colouring. It should just involve OpenMP parallelising the
assembly loop, and then each thread adds its contribution to the result
once it's processed its bunch of cells (while avoiding a race condition).

Garth



> At the end of the day I have to wait untill we support subdomains in the 
> OpenMPAssembler as I am heavily using these...
> 
> Johan
> 
> 
>> Garth
>>
>>> Johan
>>>
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>>
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