Re: [PATCH 4/5] Userspace changes for KVM HPET (v6)

[Avi Kivity <avi@redhat.com>]

Avi Kivity wrote:
> Beth Kon wrote:
>> The big change here is handling of enabling/disabling of hpet legacy 
>> mode. When hpet enters
>> legacy mode, the spec says that the pit stops generating interrupts. 
>> In practice, we want to stop the pit periodic timer from running 
>> because it is wasteful in a virtual environment.
>> We also have to worry about the hpet leaving legacy mode (which, at 
>> least in linux, happens
>> only during a shutdown or crash). At this point, according to the 
>> hpet spec, PIT interrupts
>> need to be reenabled. For us, it means the PIT timer needs to be 
>> restarted. 
>> This patch handles this situation better than the previous version by 
>> coming closer to just disabling PIT interrupts. It allows the PIT 
>> state to change if the OS modifies it,
>> even while PIT is disabled, but does not allow a pit timer to start. 
>> Then if HPET
>> legacy mode is disabled, whatever the PIT state is at that point, the 
>> PIT timer is restarted accordingly.
>>
>>   
>
> Given that this depends on the ABI-breaking patch 5, I've dropped it too.
>

Actually, I got nervous about applying a partial patchset (which is 
likely to be untested), so I dropped everything else.  I pushed the 
three patches to an 'hpet' branch of qemu-kvm.git, so you don't have to 
redo the rebasing I did.

-- 
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