Re: [Qemu-devel] Re: [Bug 599958] Re: Timedrift problems with Win7: hpet missing time drift fixups

[Jan Kiszka <jan.kiszka@web.de>]

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Gleb Natapov wrote:
> On Mon, Jul 05, 2010 at 08:49:31AM +0200, Jan Kiszka wrote:
>> Gleb Natapov wrote:
>>> On Mon, Jul 05, 2010 at 08:39:38AM +0200, Jan Kiszka wrote:
>>>> Paul Brook wrote:
>>>>>> Blue Swirl wrote:
>>>>>>> On Sat, Jul 3, 2010 at 7:39 AM, Jan Kiszka <jan.kiszka@web.de> wrote:
>>>>>>>> Paul Brook wrote:
>>>>>>>>>> I really see no tangible objection to Jan's patches.  They don't
>>>>>>>>>> impact any other code.  They don't inhibit flexibility in the
>>>>>>>>>> infrastructure. You might consider it to be a "hack" but so what. 
>>>>>>>>>> QEMU is filled with hacks.  It would be useless without them because
>>>>>>>>>> there would be very little code.
>>>>>>>>> I object strongly to anything that makes qemu_irq a message passing
>>>>>>>>> API. if you want message passing then you should not be using
>>>>>>>>> qemu_irq.
>>>>>>>> Blueswirl objected to the straightforward return-value approach I first
>>>>>>>> posted. You seems to be more open towards this, right? Still looks like
>>>>>>>> I cannot make you both happy at the same time. So what to do?
>>>>>>> I have withdrawn my objection. We can do message passing with some
>>>>>>> different API later, for simple coalescing needs the return value
>>>>>>> approach is enough.
>>>>>> Great! I'll respin my patches ASAP.
>>>>> Note that I still have some concerns over the semantics of that API.
>>>>> I believe this should be fundamentally state based, not event based.
>>>> For the caller of qemu_set_irq, it will be like that.
>>>>
>>> Unfortunately just having qemu_set_irq() return value is not enough to
>>> fix timedrift problem for all Windows. For some of them you need to know
>>> _which_ CPU accepted IRQ.
>> Return values:
>>  < 0	- no state change, specifically due to masking or latching
>>  >= 0	- first CPU (lowest index) on which a state change was achieved
>>
>> Sufficient?
>>
> To problem specific for such generic interface. Doesn't allow to
> distinguish between masking and coalescing.

It does (return values < 0 are specified to differentiate between them
and more).

> Assumes that CPU with
> lowest index is BSP (that one we can actually guaranty if we want
> to).

Well, the generic solution would be returning a bitmap of the CPUs that
were affected, but this is impractical. However, at least x86 should be
fine with the information "state change also on BSP", e.g. like this:
 0 - state change on one or more CPUs, none of them is the BSP
 1 - state change on BSP (and possible more CPUs)

> And what about PIC mode where interrupt receiver is not CPU?

In the end, there's always a CPU (or several of them).

Jan


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