Re: [Xen-devel] [RFC PATCH v2 13/22] xen/arm: its: Add virtual ITS command support

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 05/05/15 12:57, Stefano Stabellini wrote:
> On Tue, 5 May 2015, Julien Grall wrote:
>>> I think we should pause the guest vcpu until we receive
>>> the interrupt.
>>> You can do that by calling vcpu_block.
>>
>> Blocking the vcpu is not the right thing to do. The processing of the
>> ITS command queue is asynchronous and the guest may decide to execute
>> other task while waiting.
> 
> Sure, but the hypervisor might have other things to do and other vcpus
> to schedule as well. It is a matter of priorities and scheduling the
> most appropriate workload. Keep in mind that vcpu_block doesn't
> completely pause the guest, it just only blocks the vcpu until the next
> guest event occurs.

I don't think it will help to get the guest booting faster. Linux is
trying to read CREADR (The completion register) every millisecond. I
suspect we will receive an IRQ faster than that.

Regards,

-- 
Julien Grall

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