Re: [Xen-devel] Some questions about Interrupt and event channel about Xen on ARM.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Jan 2015, ììì wrote:
> 
> HiÂ
> 
> I'm studying about Xen 4.4.0 and Xen 4.5.0 on ARM
> 
> Â
> 
> I have some questions about Interrupt and event channel on ARM.Â
> 
> Â
> 
> 1.
> In Xen 4.4.X and Xen 4.5.0 (GIC v2), all pirq(physical irq) are go to pcpu0 
> (physical cpu). After pirq, Xen run in pcpu0 only
> inject virq(virtual irq) to vcpu0 of Dom0.
> I think injection of virtual irq to proper vcpu carry out interrupt load 
> balancing and reducing interrupt latency.
> Why dose Xen only route virtual to vcpu0 of Dom0? For only simple??
 
Actually Xen 4.5 is capable of routing irqs to any phsical and virtual cpus.
 Â

> 2.
> Xen 4.5.0 support GiC v3. I saw code about GICv3 in Xen 4.5.0.
> 
> it seems that GICv3 add some virq interrupt routing interface such as 
> 'GICD_IROUTER_SPI_MODE_ANY'Â
> 
> and support irq migration.ÂBut i know that 'GICv3 Architecture Specification' 
> release specification in later this year.
> How can Xen 4.5.0 Developers get GICv3 Information and where can i get GICv3 
> Information??

The specification is already available to partners.

Â
> 3.
> 
> In Xen 4.4.0, Xen occur 'GIC_SGI_EVENT_CHECK' sgi interrupt to check event 
> channel. AfterÂGIC_SGI_EVENT_CHECK sgi,
> 'leave_hypervisor_tail' function is executed on return path.
> 
> leave_hypervisor_tail function inject virq of event channel.Â
> 
> But In Xen 4.5.0,ÂAfterÂGIC_SGI_EVENT_CHECK sgi, leave_hypervisor_tail 
> dosen't injectÂvirq of event channel.
> 
> and There is no virq injectionÂof event channel on return path.Â
> 
> So I think, to sendÂGIC_SGI_EVENT_CHECK sgi is meaning less in Xen 4.5.0.

It interrups the execution of another vcpu and makes sure that the Xen
entry code is executed, including enter_hypervisor_head that calls
gic_clear_lrs.




> Right?? Am i wrong?
> 
> Â
> 
> Â
> 
> Thanks
> 
> [?img=m%2FRm%2BBFm%2BBFShAnZFAM9M6MlK4tZM6EZaxvqMoKdaxF4aAiSpAC0FzUZF4KdMvIo%2BrkSKAb5W4d5W4C5bX0q%2BzkR74FTWx%2FsDzk57630%2B4knt
> zwGbX3q7NC0WSlTb4b%3D.gif]
>

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