shared memory and event channel

shared memory and event channel

[Amit Singh]

[-- Attachment #1.1: Type: text/plain, Size: 249 bytes --]


Hi,

   For each domUs there is unique shared memory(2-way circular queue) and event-channel(one shared memory and event-channel per domU)
or there is only one shared memory and interdomain event-channel(for every DomU)?


regards:

Amit

[-- Attachment #1.2: Type: text/html, Size: 678 bytes --]

[-- Attachment #2: Type: text/plain, Size: 138 bytes --]

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

Re: shared memory and event channel

[Mark Williamson]

>    For each domUs there is unique shared memory(2-way circular queue) and
> event-channel(one shared memory and event-channel per domU) or there is
> only one shared memory and interdomain event-channel(for every DomU)?

Each domain has a separate shared memory page and event channel.  Actually, in 
general, there are multiple shared memory areas and event channels per domU.

Each virtual device (e.g. virtual network interface) may require its own 
separate shared memory page and event channel to talk to the backend.  So if 
you have a domain with two vifs it'll need two shared memory pages and two 
event channels.

The block driver will also want a memory page and event channel for each 
virtual block device.

And so on.

Hope this helps,

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

a question about xen in HVM

[tgh]

hi
  I have a question about HVM and PV, in the HVM,xen is running in the 
root mode,and should vmentry or vmexit to HVM vm,and in the PV,xen is 
running in the ring0, am i right?
  and if some PV vm and some HVM vm are running on the physical node 
with VTsupport,then which mode does the xen run in? in ring0 or what 
about it ?


Thanks in advance

Re: a question about xen in HVM

[Mark Williamson]

>   I have a question about HVM and PV, in the HVM,xen is running in the
> root mode,and should vmentry or vmexit to HVM vm,and in the PV,xen is
> running in the ring0, am i right?
>   and if some PV vm and some HVM vm are running on the physical node
> with VTsupport,then which mode does the xen run in? in ring0 or what
> about it ?

On a machine which is not VT capable, there is no "root" or "non-root" mode, 
so Xen runs in ring 0 and guests ring in rings 1-3.

On a machine which is VT capable you have "root mode" and "non-root 
mode".  "root mode" is basically the same as the normal operation of a non-VT 
processor; it still has the rings 0-3, which fulfill the same purpose as they 
did on non-VT machines.  They still work the same.  "non-root mode" is a 
second set of CPU protection rings 0-3, which Xen uses for HVM guests and 
which operate independently of those rings in "root mode".

If you're running PV and HVM guests at once then you have:

* Xen runs in ring 0 of "root mode"
* dom0 runs in ring 1-3 of "root mode"
* PV domUs run in ring 1-3 of "root mode"
* HVM domUs run in rings 0-3 of "non-root mode"

Note that when VT is available, "root mode" and "non-root" mode both have a 
set of their own rings.  So it's not a question of whether something runs in 
ring "n" anymore, it's a question of whether it runs in ring n /of root mode/ 
or ring n /of non-root mode/.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

Re: shared memory and event channel

[tgh]

hi
  I read the code of eventchannel,and I am confused by the viarable 
named as"consumer_is_xen"in the evtchn struct, what is the function of 
consumer_is_xen? and does dom use eventchannel to communicate with 
hypervisor? why not the hypercall? and in which condition is 
eventchannel used in this way,that is ,the dom issues an event to 
hypervisor or xen,and xen is a consumer?

Thanks in advance




Mark Williamson 写道:
>>    For each domUs there is unique shared memory(2-way circular queue) and
>> event-channel(one shared memory and event-channel per domU) or there is
>> only one shared memory and interdomain event-channel(for every DomU)?
>>     
>
> Each domain has a separate shared memory page and event channel.  Actually, in 
> general, there are multiple shared memory areas and event channels per domU.
>
> Each virtual device (e.g. virtual network interface) may require its own 
> separate shared memory page and event channel to talk to the backend.  So if 
> you have a domain with two vifs it'll need two shared memory pages and two 
> event channels.
>
> The block driver will also want a memory page and event channel for each 
> virtual block device.
>
> And so on.
>
> Hope this helps,
>
> Cheers,
> Mark
>
>   

Re: shared memory and event channel

[Keir Fraser]

It's a special-case type of inter-domain event channel in which one end is
connected to Xen itself rather than the guest. It's actually only used for
the per-vcpu ioemu event-channel that HVM guests require.

 -- Keir

On 21/12/07 08:39, "tgh" <wwwwww4187@sina.com.cn> wrote:

> hi
>   I read the code of eventchannel,and I am confused by the viarable
> named as"consumer_is_xen"in the evtchn struct, what is the function of
> consumer_is_xen? and does dom use eventchannel to communicate with
> hypervisor? why not the hypercall? and in which condition is
> eventchannel used in this way,that is ,the dom issues an event to
> hypervisor or xen,and xen is a consumer?
> 
> Thanks in advance
> 
> 
> 
> 
> Mark Williamson 写道:
>>>    For each domUs there is unique shared memory(2-way circular queue) and
>>> event-channel(one shared memory and event-channel per domU) or there is
>>> only one shared memory and interdomain event-channel(for every DomU)?
>>>     
>> 
>> Each domain has a separate shared memory page and event channel.  Actually,
>> in 
>> general, there are multiple shared memory areas and event channels per domU.
>> 
>> Each virtual device (e.g. virtual network interface) may require its own
>> separate shared memory page and event channel to talk to the backend.  So if
>> you have a domain with two vifs it'll need two shared memory pages and two
>> event channels.
>> 
>> The block driver will also want a memory page and event channel for each
>> virtual block device.
>> 
>> And so on.
>> 
>> Hope this helps,
>> 
>> Cheers,
>> Mark
>> 
>>   
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel