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Date: Sat, 21 Feb 2015 19:46:12 +0100
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Subject: Re: [9front] 9front on Xen 4.4 HVM
From: Giacomo Tesio <giacomo@tesio.it>
To: 9front@9front.org
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Thanks for your help cinap.  It's an interesting dive into the kernel internals.

Btw, I've tried various combinations of networks drivers (virtio-net
or rtl) and plan9.ini options but with no success.

Now I'm planning to write a plan9.ini menu with the following
configurations trying one after another looking for a working
solution.

As far as I have undestood, I should test
1) *npmp=
2) *nomsi=
3) *acpi=
and the 4 combinations of them, right?

Is there anything else that I can do to identify and fix the issue?

I assigned to the 9front guest only one cpu, to reduce the variables,
but actually, if to run on xen 9front must use a single cpu, then the
disadvantage of the pv guest will be lower, and I could give it a try
too.

Strangely, looks like I'm the first to try installing plan9 on xen in
the last few years...


Giacomo

2015-02-21 12:51 GMT+01:00  <cinap_lenrek@felloff.net>:
> well, that sounds like a interrupt problem indeed. when you send
> packets, all the driver does is to put packets in transmit ring
> and optionally kick the card with some register that it should start
> transmitting.
>
> but receiving works by the card issuing a interrupt and then the
> driver looks in the receive ring if there are new packets from the
> card.
>
> if interrupt couldnt be enabled (because if broken mp tables), then
> we wont receive anything. but sending might still work because it
> doesnt need an interrupt.
>
> the relation with mp is that mp systems use the apic interrupt
> controller instead of the legacy pic controller (it is mandatory
> as you need to use the apic to bootstrap the other processors).
>
> enabling interrupt on pic is easy. you read the irq register
> from the pci config space (that the bios programmed for you)...
> sometimes, pci interrupt router needs to be programmed.
>
> apic is a bit more complicated than pic because there can be multiple
> apic controllers (and multiple processors/lapic's) and we require
> tables (from bios) to find the mapping from pci bus interrupt
> lines to the apics (which can then be programmed to send interrupts
> to the lapics/processors).
>
> and then theres msi interrupts that *some* devices support that
> do not require any tables. you program register in pci config
> space for the device and you'r done. this also works only with
> apic.
>
> when you specify *acpi= in plan9.ini, then the kernel will use
> the acpi tables instead of the mp tables.
>
> when you use *nomp=, then we will use legacy pic interrupt controller
> and only one cpu can be used (this is also what happens when we cannot
> find mp table).
>
> --
> cinap