KVM PV DEVICES.

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August Harmon
6 years ago
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1 K DEVICES

2 Agenda Kernel Virtual Machine overview Paravirtualized s intro & brief history VirtIO Enhanced VirtIO with K support 2

3 Kernel Virtual Machine overview is a regular Linux process. K handles cpu & memory virtualization virtualizes IO devices 3

4 K Execution Model 4

5 Evolution of x86 virtualization 5

6 General & history Fully virtualized devices performs bad 55 Mbps for RTL Lots of io-exits per packet Decided to implement a modern e1000 Advantage: Only coding no guest tools involved Irq coalescing Only 2-3 io-exits per packet Can be the base of user-space But then came Ingo 6

7 architecture H guest H guest R I H frontend N guest R I G H frontend guest R N G I frontend R N I G N G frontend Linux kernel & K K 7

8 General & history V0 - leveraging Ingo Molnar s code Make loadable module Add H support Add NAPI Add memory barriers and improved ring Keep running after performance & stability Merge to the kernel? Alternatives Xen Polished s Xen specific VirtIO was just published. 8

9 VirtIO An API for virtual I/O Implements network & block logic Written by Rusty Russell Motivation Many hypervisors of all types Hard to tune and maintain each one Code reuse The K way ;) Implementations Lguest K Possible (Xen, UML,, ware?..) 9

10 VirtIO Guest kernel VIRTIO BlK Add_buf Get_buf Sync VIRTIO NET Hypervisor Specifics code Detach Restart Linux kernel & K Kick K 10 scatterlist sg[] for skb/blk_req data

11 VirtIO Hypervisor specifics The front end logic is implemented by VirtIO The needs Probing & Bus services Enumeration Irq Parameters (mac,..) Shared memory with remote side Hypercalls Host /userspace Guest kernel VIRTIO BlK Linux kernel & K K VIRTIO NET Hypervisor Specifics code 11

12 Enhanced VirtIO Reuse the reuser Motivation Increase re-use Allow operation with various bus types Make new devices code smallest Guest kernel VIRTIO BlK VIRTIO NET Hypervisor Specifics code Components Shared memory code With per hypervisor I/O hypercalls Bus (pci, virtual bus) Host Linux kernel & K K 12

13 Enhanced VirtIO Blk Net VIRTIO Net VIRTIO BlK Guest kernel Enhanced VIRTIO VIRTIO Virtual Bus Hypercalls Shared mem Linux kernel & K K 13

14 Enhanced VirtIO Status: Interface was enhanced K support PCI like configuration space added Actually we got re-used 162 LOC Guest kernel Blk Enhanced VIRTIO Virtual Bus 195 LOC Net Hypercalls VIRTIO Net VIRTIO Shared mem VIRTIO BlK Result: Makes tiny 620 Mbps throughput for network H Linux guest Before optimization Userspace Linux kernel & K K 14

15 Enhanced VirtIO shared memory VirtIO Implements VirtIO interface Callbacks to hypervisor and Code consists of add_buf, get_buf, restart, detach_buf Only shared memory logic needed sync Ring logic IO pending hypercall be_virtqueue_interrupt handler Guest kernel Blk Enhanced VIRTIO Virtual Bus Linux kernel & K Net Hypercalls VIRTIO Net VIRTIO Shared mem VIRTIO BlK K 15

16 Enhanced VirtIO Day in a life of packet Guest kernel Blk Enhanced VIRTIO Virtual Bus Net Hypercalls 3.start_xmit VIRTIO Net 4.add_buf VIRTIO 6.sync 11.irq 8.Notify hcall Shared mem VIRTIO BlK 5.add_buf 7.sync 2.Kernel Tcp/ip 1.User write 12. skb_recv_done 13. get_buf Linux kernel & K 10.Trigger irq 16 K 9.The pkts travels to tap/ host device

17 Enhanced VirtIO shared memory details Based on lguest 1-1 shared memory Data structure Page of descriptors for rx, tx. Available pointers page controlled by guest Used pointers page controlled by host SG list is currently internal to descriptors Descriptors are chained by next pointer 17

18 Enhanced VirtIO network be Implements kvm_virtnet_probe for pci bus Creates tx,rx be_new_virtqueue Probes virtnet Guest kernel Blk 195 LOC Enhanced VIRTIO Virtual Bus Net Hypercalls VIRTIO Net VIRTIO Shared mem VIRTIO BlK Request_irq Irq# taken from bus Linux kernel & K Register hypercall - shared memory pfn Device key for enumeration taken from bus K 18

19 Further work Basic Add readv/writev handlers to Complete the user-space block device Complete migration support Blk Net VIRTIO Net VIRTIO BlK Advanced (also simple) Optimize and stabilize Add host back end s Add virtual bus H improvements Test with kernel Guest kernel Enhanced VIRTIO Virtual Bus Linux kernel & K Hypercalls VIRTIO Shared mem K 19

20 Q&A Thank you ;) 20

KVM PV DEVICES.

KVM PV DEVICES. K DEVICES dor.laor@qumranet.com 1 Agenda Introduction & brief history VirtIO Enhanced VirtIO with K support Further implementation 2 General & history Fully virtualized devices performs bad 55 Mbps for