[Paraview] Parallel Streamtracer

[Stephan Rogge]

Hello,

I have a question related to the parallelism of the stream tracer: As I
understand the code right, each line integration (trace) is processed in an
own MPI process. Right? 

To test the scalability of the Stream tracer I've load a structured
(curvilinear) grid and applied the filter with a Seed resolution of 1500 and
check the timings in a single and multi-thread (Multi Core enabled in PV
GUI) situation. 

I was really surprised that multi core slows done the execution time to 4
seconds. The single core takes only 1.2 seconds. Data migration cannot be
the explanation for that behavior (0.5 seconds). What is the problem here?

Please see attached some statistics...

Data:
* Structured (Curvilinear) Grid
* 244030 Cells
* 37 MB Memory

System:
* Intel i7-2600K (4 Cores + HT = 8 Threads)
* 16 GB Ram
* Windows 7 64 Bit
* ParaView (master-branch, 64 bit compilation)

#################################
Single Thread (Seed resolution 1500):
#################################

Local Process
Still Render,  0.014 seconds
RenderView::Update,  1.222 seconds
    vtkPVView::Update,  1.222 seconds
        Execute vtkStreamTracer id: 2184,  1.214 seconds
Still Render,  0.015 seconds

#################################
Eight Threads (Seed resolution 1500):
#################################

Local Process
Still Render,  0.029 seconds
RenderView::Update,  4.134 seconds
vtkSMDataDeliveryManager: Deliver Geome,  0.619 seconds
    FullRes Data Migration,  0.619 seconds
Still Render,  0.042 seconds
    OpenGL Dev Render,  0.01 seconds


Render Server, Process 0
RenderView::Update,  4.134 seconds
    vtkPVView::Update,  4.132 seconds
        Execute vtkStreamTracer id: 2193,  3.941 seconds
FullRes Data Migration,  0.567 seconds
    Dataserver gathering to 0,  0.318 seconds
    Dataserver sending to client,  0.243 seconds

Render Server, Process 1
Execute vtkStreamTracer id: 2193,  3.939 seconds

Render Server, Process 2
Execute vtkStreamTracer id: 2193,  3.938 seconds

Render Server, Process 3
Execute vtkStreamTracer id: 2193,  4.12 seconds

Render Server, Process 4
Execute vtkStreamTracer id: 2193,  3.938 seconds

Render Server, Process 5
Execute vtkStreamTracer id: 2193,  3.939 seconds

Render Server, Process 6
Execute vtkStreamTracer id: 2193,  3.938 seconds

Render Server, Process 7
Execute vtkStreamTracer id: 2193,  3.939 seconds

Cheers,
Stephan