✎ formation:astrosim2017gpu4dummies[CBP]

✎ formation:astrosim2017gpu4dummies
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====== Practical session for Astrosim 2017 ======

Practical work support for [[https://astrosim.sciencesconf.org/|Astrosim 2017]]

===== 5 W/2H : Why ? What ? Where ? When ? Who ? How much ? How ? =====

5W/2H : CQQCOQP (Comment ? Quoi ? Qui, Combien ? Où ? Quand ? Pourquoi ?) in french...

  * **Why ?** Have a look on GPUs and improve investigations process
  * **What ?** Test with dummie examples
  * **When ?** Friday, the 7th of July in the afternoon
  * **How much ?** Nothing, Blaise Pascal Center provides GPU inside workstations & cluster nodes 
  * **Where ?** On workstations, cluster nodes, laptop (well configured), inside terminals
  * **Who ?** For people who want to open the hood 
  * **How ?** Applying some simple commands (essentially shell ones)

===== Session Goal =====
 
It's to take in the hands GPU components inside machines and compare performances to classical CPU trough simplistic examples and production codes.

===== Starting the session =====
 
==== Prerequisites hardware, software and humanware ====
 
In order to get a complete functional environment, Blaise Pascal Center provides hardware, software, and OS well designed. People who want to achieve this practical session on their own laptop must have a real Unix Operating System.

=== Prerequisite for hardware ===
 
  * If using CBP resources, nothing... Just login...
  * If NOT using CBP resources, a machine relatively recent with onboard GPU inside, Nvidia one are preferred

=== Prerequisite for software ===

  * Open graphical session on one workstation, several terminals and your favorite browser
  * If NOT using CBP resources, a GNU/Linux Operating System well configured with all GPU, Nvidia, OpenCL, PyOpenCL, PyCuda stuff

People who want to use huge GPU, GPGPU or accelerator can use connect to the following machines.
  * **gtx1080alpha**, **gtx1080beta**, **gtx1080gamma**, **gtx1080delta** : virtual workstations with dedicated Nvidia GTX 1080
  * **k80alpha**, **k80beta**, **k80gamma** : virtual workstations with dedicated one, one and two GPU inside Nvidia Tesla K80
  * **p100alpha**, **p100beta** : virtual workstations with dedicated one Nvidia Tesla P100
  * **k40m** : virtual workstations with dedicated one Nvidia Tesla K40m

=== Prerequisite for humanware === 

  * An allergy to command line will severely restrict the range of this practical session.
  * A practice of shell scripts would be a asset, but you will improve it in this session!

===== Investigate GPU Hardware =====

==== What inside my host ? ====

Hardware in computing science is defined by [[https://upload.wikimedia.org/wikipedia/commons/e/e5/Von_Neumann_Architecture.svg|Von Neumann architecture]]:
  * CPU (Central Processing Unit) with CU (Control Unit) and ALU (Arithmetic and Logic Unit)
  * MU (Memory Unit)
  * Input and Output Devices

GPU are normally considered as Input/Output devices. As mainly peripherals installed on PC machines, they use a interconnection bus, [[https://en.wikipedia.org/wiki/Conventional_PCI|PCI]] or [[https://en.wikipedia.org/wiki/PCI_Express|PCI Express]].

To get the list of PCI devices, use ''lspci -nn'' command. Inside this huge list appear some **VGA** or **3D** devices. These are GPU or GPGPU devices.

This is an output of ''lspci -nn | egrep '(VGA|3D)' '' command
<code>
06:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev ca)
82:00.0 VGA compatible controller: NVIDIA Corporation Device 1b06 (rev a1)
</code>

=== Exercice #1: get the list of (GP)GPU devices ===

  * How many VGA devices are listed ? How many 3D devices are listed ?
  * Get the model of GPU device, its long name.
  * Retreive on the www the following informations:
    * the number of compute units
    * the base frequency of the cores
    * the base frequency of the memory

All of the ''huge'' workstations hold Nvidia boards. 

In Posix operating systems, everything is file. Informations about Nvidia board and its discovery by the operating system on boot time can be get by a ''grep'' in ''dmesg''.

You can get kabalistic informations which are very important to 
<code>
[   19.545688] NVRM: The NVIDIA GPU 0000:82:00.0 (PCI ID: 10de:1b06)
               NVRM: NVIDIA Linux driver release.  Please see 'Appendix
               NVRM: A - Supported NVIDIA GPU Products' in this release's
               NVRM: at www.nvidia.com.
[   19.545903] nvidia: probe of 0000:82:00.0 failed with error -1
[   19.546254] NVRM: The NVIDIA probe routine failed for 1 device(s).
[   19.546491] NVRM: None of the NVIDIA graphics adapters were initialized!
[   19.782970] nvidia-nvlink: Nvlink Core is being initialized, major device number 244
[   19.783084] NVRM: loading NVIDIA UNIX x86_64 Kernel Module  375.66  Mon May  1 15:29:16 PDT 2017 (using threaded interrupts)
[   19.814046] nvidia-modeset: Loading NVIDIA Kernel Mode Setting Driver for UNIX platforms  375.66  Mon May  1 14:33:30 PDT 2017
[   20.264453] [drm] [nvidia-drm] [GPU ID 0x00008200] Loading driver
[   23.360807] input: HDA NVidia HDMI/DP,pcm=3 as /devices/pci0000:80/0000:80:02.0/0000:82:00.1/sound/card2/input19
[   23.360885] input: HDA NVidia HDMI/DP,pcm=7 as /devices/pci0000:80/0000:80:02.0/0000:82:00.1/sound/card2/input20
[   23.360996] input: HDA NVidia HDMI/DP,pcm=8 as /devices/pci0000:80/0000:80:02.0/0000:82:00.1/sound/card2/input21
[   23.361065] input: HDA NVidia HDMI/DP,pcm=9 as /devices/pci0000:80/0000:80:02.0/0000:82:00.1/sound/card2/input22
[   32.896510] [drm] [nvidia-drm] [GPU ID 0x00008200] Unloading driver
[   32.935658] nvidia-modeset: Unloading
[   32.967939] nvidia-nvlink: Unregistered the Nvlink Core, major device number 244
[   33.034671] nvidia-nvlink: Nvlink Core is being initialized, major device number 244
[   33.034724] NVRM: loading NVIDIA UNIX x86_64 Kernel Module  375.66  Mon May  1 15:29:16 PDT 2017 (using threaded interrupts)
[   33.275804] nvidia-nvlink: Unregistered the Nvlink Core, major device number 244
[   33.993460] nvidia-nvlink: Nvlink Core is being initialized, major device number 244
[   33.993486] NVRM: loading NVIDIA UNIX x86_64 Kernel Module  375.66  Mon May  1 15:29:16 PDT 2017 (using threaded interrupts)
[   35.110461] nvidia-modeset: Loading NVIDIA Kernel Mode Setting Driver for UNIX platforms  375.66  Mon May  1 14:33:30 PDT 2017
[   35.111628] nvidia-modeset: Allocated GPU:0 (GPU-ccc95482-6681-052e-eb30-20b138412b92) @ PCI:0000:82:00.0
[349272.210486] nvidia-uvm: Loaded the UVM driver in 8 mode, major device number 243
</code>

=== Exercice #2 : get the informations on your host with ''dmesg | grep -i nvidia'' command ===

  * What version of driver did the kernel load ?
  * What represents, if it exists, the ''input: HDA NVidia'' device ? Is it a graphical one ?

The ''lsmod'' provides the list of modules loaded. Modules are small programs dedicated to the support of on function in a kernel, the engine of the Operating System. The support of a device needs one or several modules. 

An example of ''lsmod | grep nvidia'' on a workstation:
<code>
nvidia_uvm            638976  0
nvidia_modeset        790528  2
nvidia              12312576  42 nvidia_modeset,nvidia_uvm
</code>

We see that 3 modules are loaded. The last column (empty for the two first lines) lists the dependencies between modules. Here, ''nvidia_modeset'' and ''nvidia_uvm'' depend on ''nvidia'' module.

=== Exercice #3 : get the informations on your host with ''lsmod | grep nvidia'' command ===

  * Are the informations on devices identical to the above ? Character by Character ?

The device also appears in ''/dev'' the root folder for devices. 

A ''ls -l /dev/nvidia*'' provides this kind of informations<code>
crw-rw-rw- 1 root root 195,   0 Jun 30 18:17 /dev/nvidia0
crw-rw-rw- 1 root root 195, 255 Jun 30 18:17 /dev/nvidiactl
crw-rw-rw- 1 root root 195, 254 Jun 30 18:17 /dev/nvidia-modeset
crw-rw-rw- 1 root root 243,   0 Jul  4 19:17 /dev/nvidia-uvm
crw-rw-rw- 1 root root 243,   1 Jul  4 19:17 /dev/nvidia-uvm-tools
</code>

We can see that everybody can access to the device. There is only one NVIDIA device, ''nvidia0''. On a multiple Nvidia GPU machine, we got ''nvidia0'', ''nvidia1'', etc...

=== Exercice #3 : get the informations on your host with ''dmesg | grep -i nvidia'' command ===

  * How many ''/dev/nvidia<number>'' do you get ?
  * Is this information coherent to the 3 previous commands ?

Nvidia provides information about its recognized devices via ''nvidia-smi'' command. This command can also be used to configure some tricks inside the GPU.

An example of ''nvidia-smi'' output:
<code>
Fri Jul  7 07:46:56 2017       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 375.66                 Driver Version: 375.66                    |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  GeForce GTX 108...  Off  | 0000:82:00.0      On |                  N/A |
| 23%   31C    P8    10W / 250W |     35MiB / 11172MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID  Type  Process name                               Usage      |
|=============================================================================|
|    0      4108    G   /usr/lib/xorg/Xorg                              32MiB |
+-----------------------------------------------------------------------------+
</code>

Lots of informations are available in this output:
  * version of driver and ''nvidia-smi'' software
  * the ''id'' of GPU, 
  * its name, 
  * its bus location, 
  * its fan speed, 
  * its temperature, 
  * its instantly and maximum consumption, 
  * its occupied and available
  * its processus and their location on GPU

=== Exercice #4 : get the informations with ''nvidia-smi'' command ===

  * Identify the above characteristics and compare the elements
  * How many process are listed in the bottom list ?

As we see in the introduction on GPU, programming them can be achieved with several ways. The first, for Nvidia devices, is to use CUDA environment. The problem is that it's impossible to reuse your program on other platform or compare directly with CPU. [[https://www.khronos.org/opencl/|OpenCL]] is a more agnostic way.

On the workstations in CBP, all available implementations of OpenCL are available.

The command ''clinfo'' provides informations about devices. Here is an example of a short output with ''clinfo '-l' '':
<code>
Platform #0: Clover
Platform #1: Portable Computing Language
 `-- Device #0: pthread-Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
Platform #2: NVIDIA CUDA
 `-- Device #0: GeForce GTX 1080 Ti
Platform #3: Intel(R) OpenCL
 `-- Device #0:        Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
Platform #4: AMD Accelerated Parallel Processing
 `-- Device #0: Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
</code>

  * The ''#0'' **Clover** implementation is a GPU one, based on Open Source drivers of GNU/Linux and provided by [[https://en.wikipedia.org/wiki/Mesa_%28computer_graphics%29|Mesa]]
  * The ''#1'' **Portable Computing Language** is a CPU one. Not very efficient but Open Source.
  * The ''#2'' **NVIDIA CUDA** implementation is a GPU one. The devices detected are listed below
  * The ''#3'' **Intel(R) OpenCL** implementation is a CPU one. Provided by Intel, very efficient but FP results are sometimes strange.
  * The ''#4'' **AMD Accelerated Parallel Processing** is a CPU one. Provided by AMD, rather efficient, the oldest one.

=== Exercice #5 : get the informations with ''clinfo -l'' command ===

  * Identify and compare with list above.
  * How many graphical devices do you get ?

The command ''clinfo'' without options provides lots (to much...) informations. You can restrict them for example to several attributes as ''Platform Name'',''Device Name'',''Max compute'',''Max clock''.

On the example platform, the command ''clinfo | egrep '(Platform Name|Device Name|Max compute|Max clock)' '' provides the output:<code>
 Platform Name                                   Clover
  Platform Name                                   Portable Computing Language
  Platform Name                                   NVIDIA CUDA
  Platform Name                                   Intel(R) OpenCL
  Platform Name                                   AMD Accelerated Parallel Processing
  Platform Name                                   Clover
  Platform Name                                   Portable Computing Language
  Device Name                                     pthread-Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
  Max compute units                               32
  Max clock frequency                             2401MHz
  Platform Name                                   NVIDIA CUDA
  Device Name                                     GeForce GTX 1080 Ti
  Max compute units                               28
  Max clock frequency                             1582MHz
  Platform Name                                   Intel(R) OpenCL
  Device Name                                     Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
  Max compute units                               32
  Max clock frequency                             2400MHz
  Platform Name                                   AMD Accelerated Parallel Processing
  Device Name                                     Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
  Max compute units                               32
  Max clock frequency                             1200MHz
</code>

=== Exercice #6 : get the informations with the previous and filtered ''clinfo'' command ===

  * Compare the informations between CPU implementations. Why these differencies ?
  * Compare the number of compute units to the number you find on WWW. 
  * Compare the frequencies to the frequencies found on WWW.

===== Exploration with original one : xGEMM =====

==== From BLAS to xGEMM : implementations ====

In the lecture about the GPUs, we present the GPU as a great matrix multiplier. On of the most common Linear Algebra librairies is BLAS one, formelly [[https://en.wikipedia.org/wiki/Basic_Linear_Algebra_Subprograms|Basic Linear Algebra Subprograms]].

These subprograms can be considered as //standard// one. Lots of implementations exist on all architectures. On GPU, Nvidia provides its version with [[http://docs.nvidia.com/cuda/cublas/index.html|cuBLAS]] and AMD release in Open Source its OpenCL implementation [[https://github.com/clMathLibraries/clBLAS|clBLAS]]. 

On CPU, Intel sells its optimized implementation in [[https://software.intel.com/en-us/mkl|MKL librairies]] but an Open Source equivalent, [[http://www.openblas.net/|OpenBLAS]]. Several others implementations exist and are deployed on CBP machines : [[http://math-atlas.sourceforge.net/|ATLAS]] and [[https://www.gnu.org/software/gsl/|GSL]].

The implementation on Matrix Multiply in BLAS librairies is ''xGEMM'', with ''x'' to be replaced by ''S'', ''D'', ''C'' and ''Z'' respectively for Simple precision (32 bits), Double precision (64 bits), Complex & Simple precision, Complex & Double precision.

==== Test examples  ====

Inside ''/scratch/Astrosim2017/xGEMM'' are programs implementing xGEMM for simple ''xGEMM_SP_<version>'' or double ''xGEMM_DP_<version>'':
  * ''fblas'' using ATLAS libraries
  * ''openblas'' using OpenBLAS libraries
  * ''gsl'' using GSL librairies
  * ''cublas'' using cuBLAS libraries with internal memory management
  * ''thunking'' using cuBLAS libraries with external memory management

The source code and ''Makefile'' using to compile these examples is available in tarball at:
  * on workstations: ''/scratch/AstroSim2017/xGEMM_EQ_170707.tgz''
  * on website: ''http://www.cbp.ens-lyon.fr/emmanuel.quemener/documents/Astrosim2017/xGEMM_EQ_170707.tgz''

The program call with ''-h'' option provides tiny informations to launch it. Input parameters are:
  * size of square matrix
  * number of iterations

The output provides:
  * the mean elapsed time of each cycle
  * the number of estimated GFlops
  * the error estimated by the difference between trace of matrix multiply results


 
===== Exploration with dummie codes =====

==== A GPU, a performant matrix multiplier ====

==== Pi Monte Carlo, a Compute Bound Example ====

==== NBody, a simplistic simulator ====


===== Exploration with production codes =====

==== PKDGRAV3 ====