\chapterauthor{Author Name1}{Affiliation text1}
\chapterauthor{Author Name2}{Affiliation text2}


\chapter{Introduction to CUDA}
\label{chapter2}

\section{Introduction}\label{intro}
In this chapter  we give some simple examples on CUDA  programming.  The goal is
not to provide an exhaustive presentation of all the functionalities of CUDA but
rather giving some basic elements. Of  course, readers that do not know CUDA are
invited to read other books that are specialized on CUDA programming.


\section{First example}

This first example is  intented to show how to build a  very simple example with
CUDA.   The goal  of this  example is  to performed  the sum  of two  arrays and
putting the  result into a  third array.   A cuda program  consists in a  C code
which calls CUDA kernels that are executed on a GPU.


As GPUs have  their own memory, the first step consists  in allocating memory on
the GPU. A call to \texttt{cudaMalloc} allows to allocate memory on the GPU. The
first  parameter of  this  function  is a  pointer  on a  memory  on the  device
(i.e. the GPU). In this example, \texttt{d\_} is added on each variable allocated
on the GPU meaning this variable  is on the GPU. The second parameter represents
the size of the allocated variables, this size is in bits.

In this example, we  want to compare the execution time of  the additions of two
arrays in  CPU and  GPU. So  for both these  operations, a  timer is  created to
measure the  time. CUDA proposes to  manipulate timers quick  easily.  The first
step is  to create the timer, then  to start it and  at the end to  stop it. For
each of these operations a dedicated functions is used.

In  order to  compute  the  same sum  with  a GPU,  the  first  step consits  in
transferring the data from the CPU (considered as the host with CUDA) to the GPU
(considered as the  device with CUDA).  A call  to \texttt{cudaMalloc} allows to
copy the content of an array allocated in the host to the device when the fourth
parameter is set to  \texttt{cudaMemcpyHostToDevice}. The first parameter of the
function is the destination array, the  second is the source array and the third
is the number of elements to copy (exprimed in bytes).

\putbib[biblio]

