Re: [Xen-devel] [PATCH v7 15/17] vmx: VT-d posted-interrupt core logic handling

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 09/21/2015 06:09 AM, Wu, Feng wrote:
> 
> 
>> -----Original Message-----
>> From: dunlapg@xxxxxxxxx [mailto:dunlapg@xxxxxxxxx] On Behalf Of George
>> Dunlap
>> Sent: Friday, September 18, 2015 10:34 PM
>> To: Dario Faggioli
>> Cc: Jan Beulich; George Dunlap; Tian, Kevin; Keir Fraser; Andrew Cooper;
>> xen-devel@xxxxxxxxxxxxx; Wu, Feng
>> Subject: Re: [Xen-devel] [PATCH v7 15/17] vmx: VT-d posted-interrupt core 
>> logic
>> handling
>>
>> On Fri, Sep 18, 2015 at 3:31 PM, George Dunlap
>> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>>>> As said, me too. Perhaps we can go for option 1, which is simpler,
>>>> cleaner and more consistent, considering the current status of the
>>>> code. We can always investigate, in future, whether and how to
>>>> implement the optimization for all the blockings, if beneficial and fea
>>>> sible, or have them diverge, if deemed worthwhile.
>>>
>>> Sounds like a plan.
>>
>> Er, just in case that idiom wasn't clear: Option 1 sounds like a
>> *good* plan, so unless Feng disagrees, let's go with that. :-)
> 
> Sorry for the late response, I was on leave last Friday.
> 
> Thanks for your discussions and suggestions. I have one question about option 
> 1.
> I find that there are two places where '_VPF_blocked' can get set: 
> vcpu_block()
> and do_poll(). After putting the logic in vcpu_block(), do we need to care 
> about
> do_poll(). I don't know the purpose of do_poll() and the usage case of it.
> Dario/George, could you please share some knowledge about it? Thanks a lot!

Yes, you'll need to make the callback everywhere _VPF_blocked is set.

Normally you'd want to try to refactor both of those to share a commmon
codepath, but it looks like there are specific reasons why they have to
be different codepaths; so you'll just have to make the callback in both
places (after setting VPF_blocked).

You also need to check that local_events_need_delivery() will return
"true" if you get an interrupt between that time and entering the
hypervisor.  Will that happen automatically from
hvm_local_events_need_delivery() -> hvm_vcpu_has_pending_irq() ->
vlapic_has_pending_irq()?  Or will you need to add a hook in
hvm_vcpu_has_pending_irq()?

 -George

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