During last year, we have seen the rise of LibraryOSes in the hypervisor world. Fast, scalable and light, they bring to hypervisors the resource efficiency of Containers while maintaining many of its well known isolation and manageability advantages. While most LibraryOSes are niche in what they do, OSv is designed to run almost any POSIX compliant application and just have a slight focus in the Java application. Which applications can we run? And why? What's the story with Java and what can users gain from it? And more importantly: How can Xen users and the Xen community at large benefit from OSv? Those are some of the questions that I intend to cover in this presentation.

1. OSv - A Modern Semi-POSIX LibraryOS
Glauber Costa, Lead Engineer
glommer@cloudius-systems.com

2. Typical Cloud Stack
Application
Runtime
Operating System
Hypervisor
Hardware
Protection
and
abstraction

3. Containers
Application
Runtime
Application
Runtime
Operating System
Hardware
● high simplicity
● high resource efficiency
● high performance

4. “Library OS”
Application
Runtime + OS
Application
Runtime + OS
Hypervisor
Hardware
● high simplicity
● high resource efficiency
● high performance
● high isolation

5. Architecture
● Only one application / many threads
● Single address space
● Network channels
● Written in C++11
● User API - REST
● BSD licenced
● ZFS filesystem

6. Not the only one out there
● Other examples: Erlang-on-Xen, Mirage, ClickOS.
● But runs on wide range of Hypervisors
○ Xen, KVM/Qemu, VMWare, VirtualBox.
● Supports a quasi-POSIX API.
○ no fork(), no exec(),
○ largely Linux compatible.
● Less than 1s boot time.
○ as fast as needed, not as fast as possible.

7. quasi-POSIX
● Allow unmodified applications to work,
● and modified applications to shine.

8. Performance
● System calls are free
○ context switches are really cheap ( x 4 Fedora)
● Network performance significantly faster
○ around 20 % with netperf over Fedora Linux
○ more than 50 % for some UDP workloads
● I will show you concrete results at the end

9. What do people think?
Roman Shaposhnik, Bigtop/Hadoop
"Mark my words, GridGain [...] and OSv [...] are going to
be excitingly disruptive in the next few years. […] And,
by the way, if, after reading this blog, you are not
dropping everything and porting your cloud application
to OSv, I don’t know what’s wrong with you."
http://blog.gopivotal.com/pivotal/features/pivotal-debuts-at-apachecon-north-america-2014-thanks-for-having-us

10. The Xen Situation
● We like HVM because it brings greater flexibility
○ Xen's HVM boot is really slow
○ Other than that, all other goodies are there
■ interrupt injection, pv devices, etc.
● PVH is viable, but no one looking at the moment.
○ We take patches!
● PV out of question
○ too complex,
○ technically not possible.

11. The Xen Situation - cont
Stack
Current Frame
128-byte Red Zone
region
The Xen Hypervisor does NOT
respect that!

12. Will my application be fast?
● short answer:
○ yes
● short answer 2:
○ no
● Similar to Ahmdal's law, in the context of parallelism
○ no gains for 95 % CPU hungry userspace applications
● POSIX APIs poses a limitation.

13. Fresh from the Oven
● Cassandra NoSQL
● OSv vs CentOS 7
● up to 25 % faster reads
○ 1 VCPU only

14. redis
● up to 80 % faster than
Ubuntu 14.04
○ 10 Gb networking
○ No specialized interfaces
○ we do have some problems,
though
○ check our blog about it, details at
http://osv.io/blog/

15. memcached
● unmodified,
○ brings a juicy improvement out of the box.
● modified:
○ that showcases the real performance opportunity behind OSv.
That's already ~20 %
more at http://osv.io/benchmarks/

16. To know more
http://osv.io
https://github.com/cloudius-systems/osv
@CloudiusSystems
osv-dev@googlegroups.com