Difference between revisions of "User:Pennpanda"

From Xen
Line 1: Line 1:
  +
==RTDS Scheduler==
 
===Real-Time-Deferrable-Server-Based CPU Scheduler===
+
==Real-Time-Deferrable-Server-Based CPU Scheduler==
====Introduction====
+
===Introduction===
 
The rtds scheduler is a real-time CPU scheduler built to provide guaranteed CPU capacity to real-time workload on SMP hosts. It is introduced in Xen 4.5 as an experimental scheduler.
 
The rtds scheduler is a real-time CPU scheduler built to provide guaranteed CPU capacity to real-time workload on SMP hosts. It is introduced in Xen 4.5 as an experimental scheduler.
   
====Description====
+
===Description===
Each VCPU of each domain is assigned a '''budget''' and a '''period'''. The VCPU with ('''budget''', '''period''') is supposed to have '''budget''' ms in every '''period''' ms.
+
Each VCPU of each domain is assigned a '''budget''' and a '''period'''. The VCPU with ('''budget''', '''period''') is supposed to have '''budget''' us in every '''period''' us.
   
 
Note: The VCPUs of the same domain have the same parameters right now.
 
Note: The VCPUs of the same domain have the same parameters right now.
   
====Usage====
+
===Usage===
 
The "xl sched-rtds" command can be used to tune the per VM guest scheduler parameters.
 
The "xl sched-rtds" command can be used to tune the per VM guest scheduler parameters.
 
* '''xl sched-rtds -d <domain>''' :List the parameter of the specified <domain>
 
* '''xl sched-rtds -d <domain>''' :List the parameter of the specified <domain>
 
* '''xl sched-rtds -d <domain> -p <period> -b <budget>''' : Set each VCPU's budget to <budget> and period to <period> of the specified <domain>
 
* '''xl sched-rtds -d <domain> -p <period> -b <budget>''' : Set each VCPU's budget to <budget> and period to <period> of the specified <domain>
   
====Algorithm====
+
===Algorithm===
 
The design of this rtds scheduler is as follows:
 
The design of this rtds scheduler is as follows:
   
Line 27: Line 27:
   
   
====Glossary of Terms====
+
===Glossary of Terms===
  +
*'''us''': microsecond
  +
*'''Host''': The physical hardware running Xen and hosting guest VMs.
  +
*'''VM''': Guest virtual machine.
  +
*'''VCPU''': Virtual CPU (one or more per VM).
  +
*'''CPU/PCPU''': Physical host CPU.
  +
*'''Period''': The period when a VCPU's budget is replenished or discarded.
  +
*'''Budget''': The amount of time a VCPU can execute within its period.
   
====Also See====
+
===Also See===

Revision as of 16:44, 19 December 2014

Real-Time-Deferrable-Server-Based CPU Scheduler

Introduction

The rtds scheduler is a real-time CPU scheduler built to provide guaranteed CPU capacity to real-time workload on SMP hosts. It is introduced in Xen 4.5 as an experimental scheduler.

Description

Each VCPU of each domain is assigned a budget and a period. The VCPU with (budget, period) is supposed to have budget us in every period us.

Note: The VCPUs of the same domain have the same parameters right now.

Usage

The "xl sched-rtds" command can be used to tune the per VM guest scheduler parameters.

  • xl sched-rtds -d <domain> :List the parameter of the specified <domain>
  • xl sched-rtds -d <domain> -p <period> -b <budget> : Set each VCPU's budget to <budget> and period to <period> of the specified <domain>

Algorithm

The design of this rtds scheduler is as follows:

This scheduler follows the Preemptive Global Earliest Deadline First (EDF) theory in real-time field. At any scheduling point, the VCPU with earlier deadline has higher priority. The scheduler always picks the highest priority VCPU to run on a feasible PCPU. A PCPU is feasible if the VCPU can run on this PCPU and the PCPU is idle or has a lower-priority VCPU running on it.

Each VCPU has a dedicated period and budget. The deadline of a VCPU is at the end of each period; A VCPU has its budget replenished at the beginning of each period; While scheduled, a VCPU burns its budget. The VCPU needs to finish its budget before its deadline in each period; The VCPU discards its unused budget at the end of each period. If a VCPU runs out of budget in a period, it has to wait until next period.

Each VCPU is implemented as a deferable server. When a VCPU has a task running on it, its budget is continuously burned; When a VCPU has no task but with budget left, its budget is preserved.

Queue scheme: A global runqueue and a global depletedq for each CPU pool. The runqueue holds all runnable VCPUs with budget and sorted by deadline; The depletedq holds all VCPUs without budget and unsorted.


Glossary of Terms

  • us: microsecond
  • Host: The physical hardware running Xen and hosting guest VMs.
  • VM: Guest virtual machine.
  • VCPU: Virtual CPU (one or more per VM).
  • CPU/PCPU: Physical host CPU.
  • Period: The period when a VCPU's budget is replenished or discarded.
  • Budget: The amount of time a VCPU can execute within its period.

Also See