RE: [Xen-ia64-devel] [PATCH] emulate PAL_HALT_LIGHT on domU

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Atsushi SAKAI [mailto:sakaia@xxxxxxxxxxxxxx]
>Sent: 2006年7月7日 15:27
>Hi, Kevin
>
>Sorry for late, my mail sorting was failed.
>Thanks for your comments.
>
>Anyway, I reply as follows (2items)
>
>1)mITC vITC relation in GuestOS
>
>At ParaVM GuestOS, it uses real mITC as vITC(=mITC).
>See the below(Compare the ParaVM and the FullVM)
> [...]

Yes, your observation is correct which is the current design. Later 
Same drift concept will be also required for para domain on itc drift 
platform or migration.

What I meant here is not the difference between vITM and mITM. 
Currently there're two cases to manipulate machine ITM register. 
One path is to emulate write to cr.itm for para-domain with value 
saved in domain_itm. Another is used to drive soft timer with value 
saved in itm_next. That's why vcpu_set_next_time needs to choose 
the minimal value between them, to ensure timely interrupt delivery.

However let's see your case. When para-domain is doing pal_halt_light, 
you just need to register a soft time with expiration as (domain_itm - 
current ITC) since this soft timer only serves to trigger virtual time 
interrupt for target domain. It's unnecessary to set it as (itm_next - 
current ITC) when itm_next<domain_itm, since we know vcpu timer 
not expired in this case for most time. No correctness issue, and just 
hope no waste here.

Hope clearer now. :-)

Thanks,
Kevin

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