linux-kernel - Re: hardwired VMI crap

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Date:	Thu, 08 Mar 2007 14:39:15 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	tglx@...utronix.de, Jeremy Fitzhardinge <jeremy@...p.org>,
	john stultz <johnstul@...ibm.com>, akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Pratap Subrahmanyam <pratap@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>,
	Daniel Hecht <dhecht@...are.com>,
	Daniel Arai <arai@...are.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: hardwired VMI crap

Ingo Molnar wrote:
> * Zachary Amsden <zach@...are.com> wrote:
>
>   
>> Ingo, either you or Thomas have vetoed every attempt we have made to 
>> make our code operate with clockevents. [...]
>>     
>
> this is news to me - do you have any proof of such a veto?
>   

Yes, your refusal to discuss any technical details when asked point 
blank which solution you prefer, and your continued whining and 
threatening to unmerge our code.

And I ask again for your feedback on which approach you think is correct:

1) Rewrite the interrupt subsystem of our hypervisor, making it 
incompatible with full virtualization, so that we can support an 
abstract interrupt controller with a "clean" interface
2) Reuse the same method that HPET, PIT and other time clients in i386 
use - the global_clock_event pointer which allows you to wrest control 
back from the APIC and reuse the lapic_events local clockevents.
3) Create a new low level interrupt handler for the per-cpu VMI timer 
IRQs instead of re-using the APIC handler
4) Use the irq APIs to allocate IRQ-0 as a percpu IRQ, then change the 
IO-APIC code so it can know not to convert this PIC IRQ into a IO-APIC 
edge IRQ.
5) Disable the io-apic code entirely in paravirt mode.  Rather than 
change it, merge a parallel copy of it into the VMI code
so that we can use the 99% of the code we need, with the one bugfix for 
#4 above
6) Disable the apic code entirely in paravirt mode.  Rather than change 
it, merge a parallel copy of into the VMI code so that we can use the 
90% of the code we need, with changes to the LVT0 timer handling.
7) For SMP only, allocate a non-shared IO-APIC IRQ, then after the 
IO-APIC is initialized, magically switch this to a percpu handler and 
start delivering local timer interrupts via this IRQ.
8) Create a pie-in-the-sky single interrupt source, reserve an IDT 
vector for it (or steal the lapic timer slot), and use the irq apis to 
set it up to be handled as a per-cpu interrupt.  This actually sounds 
pretty good, to me.  The only problem is we will need to switch the 
timer IRQ from IRQ 0 to this vector when the APIC is initialized, but I 
think we already have all the machinery we need to handle that.
9) ???

Zach

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