Difference between revisions of "Xen 4.2 Limits"

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== Other Limits ==
 
== Other Limits ==
* Maximum of 32K interrupts and 2k PCI segments: this limits the number of devices that can be used in two ways:  
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* Maximum of 32K interrupts and 2k PCI segments; this limits the number of devices that can be used in two ways:  
** The number of devices many can be attached to the system must fit into 2k PCI segments, i.e. 2k * 256 [buses] * 32 [devices] * 8 [functions])
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** the number of devices that can be attached to the system must fit into 2k PCI segments (i.e. 2k * 256 [buses] * 32 [devices] * 8 [functions]),
** The number of hardware interrupts they may surface (one would expect at least one interrupt per device function, so this is the stricter of the two limitations).
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** the number of hardware interrupts they may surface (one would expect at least one interrupt per device function, so this likely is the stricter of the two limitations).
  
 
[[Category:Xen]]
 
[[Category:Xen]]
 
[[Category:Xen 4.2]]
 
[[Category:Xen 4.2]]
 
[[Category:Users]]
 
[[Category:Users]]

Revision as of 08:21, 14 August 2012

Icon todo.png To Do:

This is a work in progress. Feel free to add requests for more to the talk page or add additional information here


This document contains information about limits of Xen 4.2.

CPUs & Memory

  • Xen can scale up to 4,095 host CPUs with 5Tb of RAM.
  • Using Para Virtualization (PV), Xen supports a maximum of 512 VCPUs with 512Gb RAM per guest.
  • Using Hardware Virtualization (HVM), Xen supports a maximum of 128 VCPUs with 512Gb RAM per guest.
Icon todo.png To Do:

Should this be 256 for HVM?


Note that in theory Xen supports 8192 VCPUs with PV, but event channel limitations (4k per guest) make it impossible for a guest this huge to boot, as each vCPU is expected to minimally require 2 of them (timer vIRQ and IPIs). The guest limits stated above are limits that have been tested. However, it is possibly to exceed these in theory.

Other Limits

  • Maximum of 32K interrupts and 2k PCI segments; this limits the number of devices that can be used in two ways:
    • the number of devices that can be attached to the system must fit into 2k PCI segments (i.e. 2k * 256 [buses] * 32 [devices] * 8 [functions]),
    • the number of hardware interrupts they may surface (one would expect at least one interrupt per device function, so this likely is the stricter of the two limitations).