[Adeos-main] Scheduling of different domains in Adeos

[Adeos-main] Scheduling of different domains in Adeos

[Markus Franke]

Dear Adeos Developers/Users,

while I was reading some papers about Adeos I was wondering how
scheduling is done with Adeos, if there are several domains (e.g. each
is an own operating system) working on top of it. Is there some kind of
a master-scheduler which selects the domain which is allowed to run next
based on a static priority?

Thanks for enlightment,

Markus Franke

Re: [Adeos-main] Scheduling of different domains in Adeos

[Jan Kiszka]

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Markus Franke wrote:
> Dear Adeos Developers/Users,
> 
> while I was reading some papers about Adeos I was wondering how
> scheduling is done with Adeos, if there are several domains (e.g. each
> is an own operating system) working on top of it. Is there some kind of
> a master-scheduler which selects the domain which is allowed to run next
> based on a static priority?
> 

Scheduling takes place only based on the domain priority, each time a
new asynchronous event (interrupt) arrives or a domain reports to be
idle. There is no explicit source file or function called "scheduler",
you will find its logic in the dispatching code of pipelined interrupts
and in ipipe_suspend_domain().

Jan


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Re: [Adeos-main] Scheduling of different domains in Adeos

[Markus Franke]

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Jan Kiszka wrote:
> Scheduling takes place only based on the domain priority, each time a
> new asynchronous event (interrupt) arrives or a domain reports to be
> idle. There is no explicit source file or function called "scheduler",
> you will find its logic in the dispatching code of pipelined interrupts
> and in ipipe_suspend_domain().

As far as I understood, it is possible to run more than operating system
on top of Adeos, at a time. Adeos is said to be a resource
virtualization layer and the CPU is also a resource, which has to be
shared. But if there are more than one operating system, who decides
which one get's the CPU?
The question is out of scope of the interrupt virtualization. It's just
a question about CPU virtualization.

Please correct me if I missunderstood something totally. :-)


Regards,
Markus Franke

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Re: [Adeos-main] Scheduling of different domains in Adeos

[Jan Kiszka]

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Markus Franke wrote:
> Jan Kiszka wrote:
>> Scheduling takes place only based on the domain priority, each time a
>> new asynchronous event (interrupt) arrives or a domain reports to be
>> idle. There is no explicit source file or function called "scheduler",
>> you will find its logic in the dispatching code of pipelined interrupts
>> and in ipipe_suspend_domain().
> 
> As far as I understood, it is possible to run more than operating system
> on top of Adeos, at a time. Adeos is said to be a resource
> virtualization layer and the CPU is also a resource, which has to be
> shared. But if there are more than one operating system, who decides
> which one get's the CPU?

See above: each domain (which may contain an OS) has a certain priority,
and the one with the highest priority which has events pending gets the
CPU. That's what the Adeos/I-pipe patch does on event arrival or domain
suspension.

> The question is out of scope of the interrupt virtualization. It's just
> a question about CPU virtualization.
> 
> Please correct me if I missunderstood something totally. :-)
> 

Adeos doesn't do full CPU virtualisation. Therefore, the domains must
cooperate on those resources (memory management, FPU, etc.) that aren't
switched by the nano-kernel. Adeos is not qemu or kvm, if this is what
you have in mind.

Jan


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Re: [Adeos-main] Scheduling of different domains in Adeos

[Markus Franke]

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Jan Kiszka wrote:
> See above: each domain (which may contain an OS) has a certain priority,
> and the one with the highest priority which has events pending gets the
> CPU. That's what the Adeos/I-pipe patch does on event arrival or domain
> suspension.

Ok, this I know already.

> Adeos doesn't do full CPU virtualisation. Therefore, the domains must
> cooperate on those resources (memory management, FPU, etc.) that aren't
> switched by the nano-kernel. Adeos is not qemu or kvm, if this is what
> you have in mind.

So if you want to get working more than one operating system, each
embodied in it's own domain, you have to adapt the operating systems in
order to get also some kind of CPU virtualization. But these changes are
not part of the Adeos-Patches for the Linux kernel, right?

Has anybody ever tried to set up a system with let's say two Linux
kernels working on top of Adeos, simultaneously?

Regards,
Markus

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Re: [Adeos-main] Scheduling of different domains in Adeos

[Jan Kiszka]

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Markus Franke wrote:
> Jan Kiszka wrote:
>> See above: each domain (which may contain an OS) has a certain priority,
>> and the one with the highest priority which has events pending gets the
>> CPU. That's what the Adeos/I-pipe patch does on event arrival or domain
>> suspension.
> 
> Ok, this I know already.
> 
>> Adeos doesn't do full CPU virtualisation. Therefore, the domains must
>> cooperate on those resources (memory management, FPU, etc.) that aren't
>> switched by the nano-kernel. Adeos is not qemu or kvm, if this is what
>> you have in mind.
> 
> So if you want to get working more than one operating system, each
> embodied in it's own domain, you have to adapt the operating systems in
> order to get also some kind of CPU virtualization. But these changes are
> not part of the Adeos-Patches for the Linux kernel, right?

They are included as far as Linux as root domain is concerned, i.e. the
lowest prioritised domain, hosting the whole stack.

> 
> Has anybody ever tried to set up a system with let's say two Linux
> kernels working on top of Adeos, simultaneously?

Don't know, but I also don't think so. There is still quite a difference
between stacking Linux and Xenomai on top of Adeos (with Linux as root).
Xenomai was built with the constraints of running cooperatively on top
of Linux already in mind.

Jan



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