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_ptrConst(c_char) 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()¶: Warning

the functional form of assertOnGpu() is deprecated. Please use the @assertOnGpu loop attribute instead.

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: integral)¶: Set the block size for kernels launched on the GPU.

proc gpuAtomicAdd(ref x: ?T, val: T): T¶: When run on a GPU, atomically add ‘val’ to ‘x’ and store the result in ‘x’. The operation returns the old value of x.

proc gpuAtomicSub(ref x: ?T, val: T): T¶: When run on a GPU, atomically subtract ‘val’ from ‘x’ and store the result in ‘x’. The operation returns the old value of x.

proc gpuAtomicExch(ref x: ?T, val: T): T¶: When run on a GPU, atomically exchange the value stored in ‘x’ with ‘val’. The operation returns the old value of x.

proc gpuAtomicMin(ref x: ?T, val: T): T¶: When run on a GPU, atomically compare ‘x’ and ‘val’ and store the minimum in ‘x’. The operation returns the old value of x.

proc gpuAtomicMax(ref x: ?T, val: T): T¶: When run on a GPU, atomically compare ‘x’ and ‘val’ and store the maximum in ‘x’. The operation returns the old value of x.

proc gpuAtomicInc(ref x: ?T, val: T): T¶: 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’. Otherwise x is set to 0. The operation returns the old value of x.

proc gpuAtomicDec(ref x: ?T, val: T): T¶: 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. Otherwise x is set to val. The operation returns the old value of x.

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

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

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

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

proc gpuSumReduce(const ref A: [] ?t)¶

Add all elements of an array together on the GPU (that is, perform a sum-reduction). The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Only arrays with int, uint, and real types are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4]; // will be GPU-accessible
  writeln(gpuSumReduce(Arr)); // 15
}

proc gpuMinReduce(const ref A: [] ?t)¶

Return the minimum element of an array on the GPU (that is, perform a min-reduction). The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Only arrays with int, uint, and real types are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4]; // will be GPU-accessible
  writeln(gpuMinReduce(Arr)); // 1
}

proc gpuMaxReduce(const ref A: [] ?t)¶

Return the maximum element of an array on the GPU (that is, perform a max-reduction). The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Only arrays with int, uint, and real types are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4]; // will be GPU-accessible
  writeln(gpuMaxReduce(Arr)); // 5
}

proc gpuMinLocReduce(const ref A: [] ?t)¶

For an array on the GPU, return a tuple with the value and the index of the minimum element (that is, perform a minloc-reduction). If there are multiple elements with the same minimum value, the index of the first one is returned. The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Only arrays with int, uint, and real types are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4]; // will be GPU-accessible
  writeln(gpuMinLocReduce(Arr)); // (1, 2). Note that Arr[2]==1.
}

proc gpuMaxLocReduce(const ref A: [] ?t)¶

For an array on the GPU, return a tuple with the value and the index of the maximum element (that is, perform a maxloc-reduction). If there are multiple elements with the same maximum value, the index of the first one is returned. The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Only arrays with int, uint, and real types are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4]; // will be GPU-accessible
  writeln(gpuMaxLocReduce(Arr)); // (5, 3). Note that Arr[3]==5.
}

proc gpuScan(ref gpuArr: [] ?t) where isNumericType(t) && !isComplexType(t)¶

Calculates an exclusive prefix sum (scan) of an array on the GPU. The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Arrays of numeric types are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4]; // will be GPU-accessible
  gpuScan(Arr);
  writeln(Arr); // [0, 3, 5, 6, 11]
}

proc gpuSort(ref gpuInputArr: [] uint)¶

Sort an array on the GPU. The array must be in GPU-accessible memory and the function must be called from outside a GPU-eligible loop. Only arrays with uint eltType are supported. A simple example is the following:

on here.gpus[0] {
  var Arr = [3, 2, 1, 5, 4] : uint; // will be GPU-accessible
  gpuSort(Arr);
  writeln(Arr); // [1, 2, 3, 4, 5]
}