Lesson 3c (CPU and Device Virtualization) Flashcards
What two schedulers does the hypervisor use
proportional and fair share
what is the proportional share scheduler based on
Service level agreement. We could give guest1 50% guest2 30% and guest3 20%
what is the fair share scheduler based on
all guest get the same share if we had 3 guest they would get 33% each
what does the hypervisor need to do to handle cpu instructions that fail silently outside of privileged mode
It inspects the binary and rewrites the instructions to equivalent instructions that do not fail silently
how are devices communicated with in full virtualized
trap and emulate
how are devices communicated with in para virtualization
more opportunities for innovation. explict (hypercalls) “guest has control”
data transfer ni full virtualization
implicit
data transfer in para vitualization
explicit. async I/O rings
What is the I/O Ring
it is a circular data structure that the guest uses to talk to the para hypervisor
How does adding request to the ring work
It is producer consumer where the guest produces. It has a share pointer with xen on where to add records
how does adding responses work
Producer consumer is used. Xen owns a shared pointer with the guest. the guest can only read this pointer. The pointer is updated when responses are written. The guest has a share pointer that it uses to know where in the rung to pull data from.
In network virtualization how many I/O rings does Xen have?
two. One for transmit and one for receving
are the packets copied into the I/O ring
No. a shared pointer is enqued
what scheduling algorithm does xen use for networking
Round robin amoung virtual machines
where do the packets that are received go
Xen preallocates frames from the guest OS and has pointers to these pages in the receive ring. The packets are inserted in these frames
how does xen make disk I/O efficent
Request from competing domains may be reordered
are the disk i/o pages copied to the ring
No. they are accessed via shared pointers that are in the ring
what is a “reorder barrier”
allows the guest to enforce order of i/o operations
What time measurement do virtual machins need for billing
cpu, memory, storage and network usage
what is the difference between virtual and extensible OS?
Focus is on protection and flexibility
what is hardware assisted virtualization
technique xen uses to run unmodified OS. (xen is normally para)
