Re: [PATCH] kvm-userspace: Make PC speaker emulation aware of in-kernel PIT

Jan Kiszka
2009-04-25T16:28:17Z

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Anthony Liguori wrote:
> Marcelo Tosatti wrote:
>> Jan,
>>
>> While the patch itself looks fine, IMO it would be better to move all
>> of the timer handling to userspace, except the performance critical
>> parts,
>> since most of it is generic. Either periodic or one-shot timer, with:
>>
>
> The reason for having the PIT in-kernel is not performance. The PIT is
> not performance sensitive.

I think that depends. Some OSes (in some configurations) use the PIT
counter as clock source and/or program it regularly in one-shot mode. An
aging use case, but still a valid one.

>
> It's because it was easier to do interrupt catch-up by pushing the PIT
> into the kernel which IMHO was the wrong path to go down.

Pushing the emulation of port 0x61 into the kernel was a mistake we now
have to deal with. I'm not that sure about the PIT itself.

Jan

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