Unlimited Event Channels David Vrabel 24 October 2013 What are - - PowerPoint PPT Presentation

▶
unlimited event channels
SMART_READER_LITE
LIVE PREVIEW

Unlimited Event Channels David Vrabel 24 October 2013 What are - - PowerPoint PPT Presentation

Aug 21, 2023 10 likes •144 views

Unlimited Event Channels David Vrabel 24 October 2013 What are Event Channels? Paravirtual interrupts Edge triggered Bidirectional Directed at a single VCPU 24 October 2013 Unlimited Event Channels 2 / 13 How do

slide-1
SLIDE 1

“Unlimited” Event Channels

David Vrabel 24 October 2013

slide-2
SLIDE 2

What are Event Channels?

◮ Paravirtual interrupts ◮ Edge triggered ◮ Bidirectional ◮ Directed at a single VCPU

24 October 2013 “Unlimited” Event Channels 2 / 13

slide-3
SLIDE 3

How do Event Channels Work?

Domain B Domain A Shared Memory Notify Set Pending Upcall

1 2 3 4

Call Handlers Xen

24 October 2013 “Unlimited” Event Channels 3 / 13

slide-4
SLIDE 4

Original (2-Level) Design

Masked Pending ... ... ... ... ... ... ... Selector Shared Memory Per-VCPU Shared Memory 4096 bits 64 bits 64 bits 1 1 1

24 October 2013 “Unlimited” Event Channels 4 / 13

slide-5
SLIDE 5

Problems

◮ Too few ◮ No priorities ◮ Unfair

24 October 2013 “Unlimited” Event Channels 5 / 13

slide-6
SLIDE 6

Additional Requirements

◮ Identical ABI between 32-bit and 64-bit guests ◮ Reasonable memory usage ◮ Easily extensible

24 October 2013 “Unlimited” Event Channels 6 / 13

slide-7
SLIDE 7

New (FIFO-based) Design

P M L LINK 1 1 1 1 1 1 6 3 Up to 132,072 words 1 ... HEAD READY Per-VCPU shared memory Shared memory

Port 0

(Reserved)

1 2 3 4 5 6 7 Bit 15 1 Priority 0 1 15

1

Bit 31 30 29 16 ... 24 October 2013 “Unlimited” Event Channels 7 / 13

slide-8
SLIDE 8

Raising an Event

function raise(q, p) E[p].pending = 1 if not E[p].masked and not E[p].linked E[p].linked = 1 if T[q] != p linked = link(T[q], p) else linked = false if not linked C.head[q] = p T[q] = p

  • 1. Set pending
  • 2. Unmasked and not in list?

Add to list

  • 3. Set LINK of tail
  • r

Set HEAD in control block

  • 4. Advance tail

24 October 2013 “Unlimited” Event Channels 8 / 13

slide-9
SLIDE 9

Handling an Event

function handle_one_event(q) p = H[q] if p == 0 p = C.head[q] link = unlink(p) H[q] = link if E[p].pending and not E[p].masked handle(p)

  • 1. Get local head
  • 2. List was empty?

Get new HEAD from control block

  • 3. Clear LINKED and LINK
  • 4. Advance local head
  • 5. Pending and unmasked?

Handle IRQ

24 October 2013 “Unlimited” Event Channels 9 / 13

slide-10
SLIDE 10

Event Channel Fairness

500 1000 1500 2000 2500 3000 75 80 85 90 Latency (ns) Event Channel Port 2-Level FIFO-based

24 October 2013 “Unlimited” Event Channels 10 / 13

slide-11
SLIDE 11

Current Status

◮ Xen support in 4.4 ◮ Linux support in 3.14

24 October 2013 “Unlimited” Event Channels 11 / 13

slide-12
SLIDE 12

Further Work

◮ Investigate how priorities may be used ◮ Add support for limiting number of event channels to other toolstacks (XAPI,

libvirt)

◮ Add support in other OSes ◮ Xen event lock scalability ◮ Linux PIRQ setup/teardown refactoring

24 October 2013 “Unlimited” Event Channels 12 / 13

slide-13
SLIDE 13

Questions?

◮ Design Document

http://xenbits.xenproject.org/people/dvrabel/event-channels-F.pdf

24 October 2013 “Unlimited” Event Channels 13 / 13