Re: [Qemu-devel] [PATCH uq/master] kvm: Drop unused kvm_pit_in_kernel

[Jan Kiszka]

On 2012-03-22 13:52, Gleb Natapov wrote:
> On Thu, Mar 22, 2012 at 01:41:18PM +0100, Jan Kiszka wrote:
>> On 2012-03-22 08:18, Gleb Natapov wrote:
>>> On Wed, Mar 21, 2012 at 02:49:09PM +0100, Jan Kiszka wrote:
>>>> On 2012-03-21 14:41, Gleb Natapov wrote:
>>>>> On Wed, Mar 21, 2012 at 02:39:47PM +0100, Jan Kiszka wrote:
>>>>>> On 2012-03-21 14:36, Avi Kivity wrote:
>>>>>>> On 03/21/2012 02:36 PM, Jan Kiszka wrote:
>>>>>>>> This is now implied by kvm_irqchip_in_kernel.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> So we can't have -no-kvm-pit?
>>>>>>>
>>>>>>> No huge loss, but unexpected.
>>>>>>
>>>>>> See e81dda195556e72f8cd294998296c1051aab30a8.
>>>>>>
>>>>> I am curious what is the reason for upstream to not supporting disabling 
>>>>> the
>>>>> in-kernel PIT separately?
>>>>
>>>> It was considered no longer relevant:
>>>> http://thread.gmane.org/gmane.comp.emulators.kvm.devel/85393
>>>>
>>> Hmm, may be we should think about this some more. If in the (not so far)
>>> future we want to drop pit emulation from the kernel we may want to support
>>> -no-kvm-pit to allow migration from old kernels to new one.
>>
>> That's not an issue. Both device models are compatible, and you can
>> migrate between kernel_irqchip=on/off theses days with QEMU.
>>
> Cool. Including PIT lost tick compensation?

The feature is not yet available for the userspace PIT (we only support
tick compensation for the userspace RTC - IIRC). Requires better IRQ
injection feedback, you likely remember. ;)

Also, I wonder if the kernel exports all tick-compensation related
states for save/restore. Need to check again...

Jan

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