Eliot Miranda wrote:
Hi Ben,
On Dec 19, 2014, at 8:08 PM, Ben Coman <[email protected]> wrote:
Just some thoughts that arose as I skipped along the web...
With the idea of using Pharo in the cloud, I was thinking of how PharoNOS[1] is
basing off top of the Linux kernel, but the examples indicate its operating in
User Mode. So I was wondering about performance being greater[2] if the CogVM
ran in Kernel Mode. However maybe this could get tangled in the GPL license of
the kernel.
Now I believe FreeBSD/NetBSD license is compatible with COG's MIT license, so
that seems a better option for eliminating layers of the operating system.
They both[3][4] have pre-built Amazon Machine Images to run on EC2, as well as
instructions[5] to build your own AMI. So potentially we could build an AMI
with the CogVM linked to the FreeBSDKernel operating in Kernel Mode, with no
User Mode. The lack of direct access to memory from the Image, and probably
single application focus should be sufficient security to forgo User Mode, and
run faster.
But we could go a step further. Runing in the cloud relies heavily on
virtualisation, and for performance[6], most likely on the OS's
paravirtualisation interface - to Xen for example. So from Cog, why not
interface direct to the Xen FrontEndDriver[7] and eliminate the DomU operating
system all together. What I understand from [6] is that Xen's
paravirtualisation hooks makes it much easier to boot, than booting on the bare
metal of a fully-virtualised system. So the former seems more achievable than
the latter (which was the only option in years past), and also be more portable
as technology evolves, to any platform Xen runs on.
Squeak/Pharo on Cog-Xen could be a good choice for a Cloud Operating System[8].
Maybe a good student research project?
This sounds really cool, but could you analyse a bit further?
- what key economic and managerial benefits accrue from this configuration?
I'll put some more thought into this, but just off the top of my head
(so it turned out more technical than economic/managerial):
* Eliminates performance overhead of system call context switching.
Although this is replaced by hypercalls, it removes one layer on
hypervisor systems, which plausibly is going to be EVERYTHING in the future.
* Eliminate performance overhead of OS networking stack
http://roscidus.com/blog/blog/2014/08/15/optimising-the-unikernel/
* Data from virtual devices is event driven.
* More easily portable to different ARM platforms. Xen will present a
common interface to hide platform idiosyncrasies.
--> More widespread embedded use Cog.
http://www.slideshare.net/xen_com_mgr/free-rtos-xensummit
* Run databases in their own domain.
* Isolate plugin memory space. Rather than linking plugins into Cog,
potentially threatening its stability, run them in a separate domain and
use high-speed inter-domain shared memory.
http://www.cs.ucsb.edu/~nanli/projects/cs270.pdf
* Have a cloud community of thousands** of Images running each in their
own domain, communicating with high-speed inter-domain shared memory.
** presumptive figure - would need to check scaling ability
* Data sharing on high density hosting providers. Not sure if its there
yet, but may get Copy-On-Write
http://www-archive.xenproject.org/files/xensummit_fall07/18_GregorMilos.pdf
* In very large Images, which Spur will allow, perhaps a better way to
snapshot an Image is via virtual machine snapshotting using Copy-On.
http://www.cercs.gatech.edu/tech-reports/tr2010/git-cercs-10-05.pdf
* Rather than convert the Cog/Image to be multi-threaded, could have
many grid nodes running their own domain, communicating with high speed
shared memory.
http://www.cs.ucsb.edu/~nanli/projects/cs270.pdf
http://osnet.cs.binghamton.edu/publications/hines07memx.pdf
* AMD's hardware virtualisation eliminated a Ring and also segmented
memory protection used by virtualisation to separate address spaces, so
64-bit AMD can be slower. Eliminating the OS kernel layer probably
bypasses this limitation since there would be only two levels -
Hypervisor & Cog.
https://lse.epita.fr/data/2011-lse-summer-week/xen.pdf
* Its where all the cool kids hang out --> marketing opportunity
- what infrastructure is missing? (e.g. what key drivers need implementing?)
I'll need to understand Cog more. As a start, here are some porting and
API docs...
http://events.linuxfoundation.org/sites/events/files/slides/Porting%20FreeBSD%20on%20Xen%20on%20ARM%20.pdf
http://oss.org.cn/ossdocs/server_storage/xen/interface/interface.html
http://www.informit.com/articles/article.aspx?p=1160234&seqNum=4
https://lse.epita.fr/data/2011-lse-summer-week/xen.pdf
https://github.com/cloudius-systems/osv/blob/master/drivers/xenfront-xenbus.cc
cheers -ben
[1] http://pillarhub.pharocloud.com/hub/mikefilonov/pharonos
[2] http://blog.codinghorror.com/understanding-user-and-kernel-mode/
[3] http://www.daemonology.net/freebsd-on-ec2/
[4] http://wiki.netbsd.org/amazon_ec2/amis/
[5] http://wiki.netbsd.org/amazon_ec2/build_your_own_ami/
[6] http://wiki.xen.org/wiki/Virtualization_Spectrum
[7] http://wiki.xen.org/wiki/FrontendDriver
[8] http://wiki.xen.org/wiki/Cloud_Operating_Systems
Eliot (phone)
