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

[Avi Kivity <avi@redhat.com>]

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.

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