.. title: PAR Class 12, Mon 2021-03-08
.. slug: class12
.. date: 2021-03-08
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Types of virtualization
-----------------------

#. There are many possible levels of virtualization.

#. At a low level, one might emulate the HW.  This is quite flexible but too slow.

#. At a higher level, a basic OS runs separate virtual machines, each with its own file system.

   a. Harmless machine instructions execute normally.

   #. Powerful ones are trapped and emulated.

   #. This requires a properly designed instruction set.

   #. IBM has been doing this commercially for 40 years, with something originally called CP/CMS.

   #. I think that IBM lucked out with their instruction set design, and didn't plan it.

   #. Well-behaved clients might have problematic code edited before running, to speed the execution.

   #. I think that Vmware does that.

   #. It seems that compute-intensive clients might have almost no overhead.

   #. However, the emulated file system can be pretty bad.

   #. With Vmware, several clients can all be different OSs, and the host can be any compatible OS.

   #. E.g., I've had a linux vmware host simultaneously running both linux and windows clients.

   #. SFAIK, Vmware currently doesn't run on Ubuntu because of recent linux security upgrades requiring that new modules installed in the kernel be signed.

   #. In linux, root no longer has infinite power.

#. The next level of virtualization has an nontrivial host OS, but separates the clients from each other.

   #. They see a private view of the process space, file system, and other resources.

   #. This is lighter weight, e.g., quicker to start a VM and less overhead.

   #. The host and client must be the same OS.

   #. This might be called paravirtualization.

   #. Linux supports this with things like namespace isolation and control groups (cgroups).  Wikipedia et al describe this.


#. The next level up is the normal linux security.

   a. You can see all the processes and similar resources.

   #. The file system has the usual protections.

   #. This is hard to make secure when doing something complicated.

   #. How do I protect myself from firefox going bad?

   #. It's easy to describe what it should be allowed to do, but almost impossible to implement.

   #. That includes using apparmor etc.

#. In theory, packaging an app in a virtual machine has fewer dependencies and is more secure.

#. You can run the vm w/o changes on different hosts.

#. A Vmware client can run w/o change on both linux and windows hosts.

#. You can run a client on your own hardware, then spill over to a commercial cloudy platform when necessary.
     
   
Docker 
------------------

#. Docker is a popular lightweight virtualization system, which Nvidia uses to distribute SW.

#. Docker runs **images** that define virtual machines.

#. Docker images share resources with the host, in a controlled manner.

#. For simple images, which is not nvidia/cuda, starting the image is so cheap that you can do it to run one command, and encapsulate the whole process in a shell function.

#. Docker is worth learning, apart from its use by Nvidia for parallel computing.   You might also look up Kubernetes.

#. More info:

   #. https://www.docker.com/

   #. https://www.zdnet.com/article/what-is-docker-and-why-is-it-so-darn-popular/

   #. https://opensource.com/resources/what-docker

#. I installed docker on parallel to run nvidia images like pgc++.  Then I removed it because it wasn't necessary, was complicated, and it was insecure.



Nvidia GPU and accelerated computing, 6
---------------------------------------

This is from https://developer.nvidia.com/teaching-kits-downloads

My local copy of what I'm using is in /parclass/2021/files/nvidia/GPU-Teaching-Kit-Accelerated-Computing.zip

Today we'll start from
Module_9_Parallel_Computation_Patterns_Reduction/Slides/Lecture-9-1-reduction.pdf

This introduces some common parallel programming paradigms.

Today we did thru 10-2.