Re: [Xen-devel] [PATCH] Remove a set operation for VCPU_KICK_SOFTIRQ when post interrupt to vm.

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> 09/18/15 2:29 AM >>>
>Zhang, Yang Z wrote on 2015-09-08:
>I have a quick check on current code. I am curious that is current Xen
> preemptive?

> Also, when return from an interrupt handler, hypervisor didn't check
> whether reschedule is needed if the interrupt is occurred in kernel context.
>ENTRY(ret_from_intr)
        >GET_CURRENT(%rbx)
        >testb $3,UREGS_cs(%rsp)
        >jz    restore_all_xen              //call iret directly to restore 
previous context where interrupt occur if it is in kernel space.

>If Xen isn't preemptive, the above case I mentioned should never happen since
> the VCPU still run in the same PCPU. Am I right?

I have to admit that I don't see the connection to preemptiveness: The reference
above is to a code section with interrupts disabled.

Jan


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