PMacc data types [Buffer]

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This page gives an overview of the data containers in PMacc.

Their according iterators are called Box(es) in PMacc.

Naming

Buffer is a container that holds or points to memory

Array Based Buffers

• array buffers are located in libPMacc/include/memory/buffers
• buffers:
  • are container of real memory, which is located on either an accelerator/host or both
  • or can be constructed from a combination of other buffers

Buffers with Real Memory

In the most cases buffer types are a combination of [memory location]Buffer (the interface), Buffer (generic interface) and [memory location]BufferIntern (implementation).

• DeviceBuffer/ DeviceBufferIntern
  • contains device memory
  • memory is set to zero on initialization
  • line by line aligned (if multi dimensional)
  • number of elements (current size) is available on device (optional)
  • can point to existing device memory (optional)
• HostBuffer/ HostBufferIntern
  • contains host memory
  • memory is set to zero on initialization
  • multi dimensional memory is not aligned
• Exchange/ExchangeIntern
  • buffer to communicate guarding cells (ghost cells)
  • contains host buffer
  • points to a subset of an existing device buffer (host and device size are the same)
  • linear device double buffer of subset were the device buffer points to (only existing on multi dimensional exchanges) [ used to speed up memory copies from host2device and device2host ]
• MappedBuffer
  • contains host buffer that can be accessed directly from a device
  • memory is set to zero on initialization
  • same interface like DeviceBuffer
  • not aligned

Combined Buffers

• GridBuffer
  • complex buffer that contains a DeviceBuffer and a HostBuffer
  • ExchangeBuffer can be added at runtime for every surface of the memory (1D -- <=2 exchanges, 2D -- <= 8 exchanges, 3D -- <=26 exchanges)
  • contains methods for asynchronous communication of the exchanges
  • definition: GridBuffer<DataType, DIM1> *myGridBuffer; (psychocoderHPC: we shouln't show interfaces in the WIKI, maybe we can add a example code section here?)
  • initialization: myGridBuffer = new GridBuffer<DataType, DIM1 > (DataSpace<DIM1 > (NumberOfElements));
  • copy to host: myGridBuffer->deviceToHost();
  • get pointer to memory on host: myGridBuffer->getHostBuffer().getBasePointer()
  • get pointer to memory on the device: myGridBuffer->getDeviceBuffer().getDataBox()
  • free buffer: __delete(myGridBuffer);
  • delete data on device: myGridBuffer->getDeviceBuffer().reset(false);
• MultiGridBuffer
  • creates multiple GridBuffers of the same native data type and size in one big memory chunk
  • every GridBuffer can be accessed by an enum
  • exchanges can be set separately for one GridBuffer or for all
  • the used iterator MultiBox has a small memory footprint in contrast to multiple GridBuffers

Particle Buffers

Particle buffers are located in libPMacc/include/particles/memory/buffers

• HeapBuffer
  • not longer needed and supported after we switched to the memory controller mallocMC
• RingBuffer
  • not longer needed and supported after we switched to the memory controller mallocMC
• StackExchangeBuffer
  • ???
• ParticleBuffer
  • cool stuff