GPU¶

Usage

use GPU;

or

import GPU;

Supports utility functions for operating with GPUs.

Warning

This module is unstable and its interface is subject to change in the future.

GPU support is a relatively new feature to Chapel and is under active development.

For the most up-to-date information about GPU support see the technical note about it.

proc gpuWrite(const args ...?k)¶

This function is intended to be called from within a GPU kernel and is useful for debugging purposes.

Currently using write to send output to stdout will make a loop ineligible for GPU execution; use gpuWrite instead.

Currently this function will only work if values of type c_string are passed.

On NVIDIA GPUs the written values will be flushed to the terminal after the kernel has finished executing. Note that there is a 1MB limit on the size of this buffer.

proc gpuWriteln(const args ...?k)¶: Pass arguments to gpuWrite and follow with a newline.

proc assertOnGpu()¶: Will halt execution at runtime if called from outside a GPU. If used on first line in foreach or forall loop will also do a compile time check that the loop is eligible for execution on a GPU.

proc gpuClock(): uint¶: Returns value of a per-multiprocessor counter that increments every clock cycle. This function is meant to be called to time sections of code within a GPU enabled loop.

proc gpuClocksPerSec(devNum: int)¶: Returns the number of clock cycles per second of a GPU multiprocessor. Note: currently we don’t support calling this function from within a kernel.

proc syncThreads()¶: Synchronize threads within a GPU block.

proc createSharedArray(type eltType, param size): c_ptr(eltType)¶

Allocate block shared memory, enough to store size elements of eltType. Returns a CTypes.c_ptr to the allocated array. Note that although every thread in a block calls this procedure, the same shared array is returned to all of them.

Arguments

eltType – the type of elements to allocate the array for.
size – the number of elements in each GPU thread block’s copy of the array.

proc setBlockSize(blockSize: int)¶: Set the block size for kernels launched on the GPU.

proc gpuAtomicAdd(ref x: ?T, val: T): void¶: When run on a GPU, atomically add ‘val’ to ‘x’ (result is stored in ‘x’).

proc gpuAtomicSub(ref x: ?T, val: T): void¶: When run on a GPU, atomically subtract ‘val’ from ‘x’ (result is stored in ‘x’).

proc gpuAtomicMin(ref x: ?T, val: T): void¶: When run on a GPU, atomically compare ‘x’ and ‘val’ and store the minimum in ‘x’.

proc gpuAtomicMax(ref x: ?T, val: T): void¶: When run on a GPU, atomically compare ‘x’ and ‘val’ and store the maximum in ‘x’.

proc gpuAtomicInc(ref x: ?T, val: T): void¶: When run on a GPU, atomically increments x if the original value of x is greater-than or equal to val, if so the result is stored in ‘x’.

proc gpuAtomicDec(ref x: ?T, val: T): void¶: When run on a GPU, atomically determine if ‘x’ equals 0 or is greater than ‘val’. If so store ‘val’ in ‘x’ otherwise decrement ‘x’ by 1.

proc gpuAtomicAnd(ref x: ?T, val: T): void¶: When run on a GPU, atomically perform a bitwise ‘and’ operation on ‘x’ and ‘val’ and store the result in ‘x’.

proc gpuAtomicOr(ref x: ?T, val: T): void¶: When run on a GPU, atomically perform a bitwise ‘or’ operation on ‘x’ and ‘val’ and store the result in ‘x’.

proc gpuAtomicXor(ref x: ?T, val: T): void¶: When run on a GPU, atomically perform a bitwise ‘xor’ operation on ‘x’ and ‘val’ and store the result in ‘x’.

proc gpuAtomicCAS(ref x: ?T, cmp: T, val: T): void¶: When run on a GPU, atomically compare the value in ‘x’ and ‘cmp’, if they are equal store ‘val’ in ‘x’.