Re: [Qemu-devel] [PATCH] kvm: ioapic: conditionally delay irq delivery during eoi broadcast

[Zhang Haoyu]

>> Subject: [Qemu-devel] [PATCH] kvm: ioapic: conditionally delay irq delivery
>> duringeoi broadcast
>> 
>> Currently, we call ioapic_service() immediately when we find the irq is still
>> active during eoi broadcast. But for real hardware, there's some dealy 
>> between
>> the EOI writing and irq delivery (system bus latency?). So we need to emulate
>> this behavior. Otherwise, for a guest who haven't register a proper irq 
>> handler
>> , it would stay in the interrupt routine as this irq would be re-injected
>> immediately after guest enables interrupt. This would lead guest can't move
>> forward and may miss the possibility to get proper irq handler registered 
>> (one
>> example is windows guest resuming from hibernation).
>> 
>> As there's no way to differ the unhandled irq from new raised ones, this 
>> patch
>> solve this problems by scheduling a delayed work when the count of irq 
>> injected
>> during eoi broadcast exceeds a threshold value. After this patch, the guest 
>> can
>> move a little forward when there's no suitable irq handler in case it may
>> register one very soon and for guest who has a bad irq detection routine ( 
>> such
>> as note_interrupt() in linux ), this bad irq would be recognized soon as in 
>> the
>> past.
>> 
>> Cc: Michael S. Tsirkin <address@hidden>
>> Signed-off-by: Jason Wang <address@hidden>
>> Signed-off-by: Zhang Haoyu <address@hidden>
>> ---
>>  include/trace/events/kvm.h | 20 +++++++++++++++++++
>>  virt/kvm/ioapic.c          | 50
>> ++++++++++++++++++++++++++++++++++++++++++++--
>>  virt/kvm/ioapic.h          |  6 ++++++
>>  3 files changed, 74 insertions(+), 2 deletions(-)
>> 
>If this is a new version, please add a v2/v3 suffix and describe the changes at
>those different versions .
>
>You can get more information from:
>http://wiki.qemu.org/Contribute/SubmitAPatch
>
Okay, thanks.

>Best regards,
>-Gonglei