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RE: [Xen-devel] [PATCH 2/3][RFC] MSI/MSI-X support fordom0/driverdomain

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH 2/3][RFC] MSI/MSI-X support fordom0/driverdomain
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Mon, 28 May 2007 20:12:37 +0800
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Thread-topic: [Xen-devel] [PATCH 2/3][RFC] MSI/MSI-X support fordom0/driverdomain
>From: Tian, Kevin
>Sent: 2007年5月28日 20:04
>>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>>Sent: 2007年5月28日 19:48
>>Xen doesn't give a crap about the pirq namespace, except for subtle
>>semantics associated with legacy isa irqs 0-15. Or at least, what little
>>care it does have can (and likely will) be removed. So it's up to dom0
>>whether it wants its pirq namespace to correspond to BIOS-assigned
>>usual Linux allocation scheme, GSI space, or whatever. This interface
>>let dom0 control how MSI and INTx is plumbed into its pirq space, if
>>what it wants. Other domUs will have no need for an association
>>their pirq namespace and physical hardware/bios irq numbering -- in
>>case it may make sense to leave it to Xen to do the allocation. But even
>>here, the interface as I described it would allow dom0 to have control
>>domU allocation too if it wants it.
>> -- Keir
>OK, I agree it's flexible and extensible. But is there any real usage
>model pushing on this? For example, is it better for pciback instance
>to allocate pirq space for domU? Pciback can select whether
>passthrough real irq number or allocate from a new space for
>target domain. To let Xen allocate instead makes it complex.

My point is:
        - Xen itself doesn't take any usage of per-domain pirq namespace
        - Dom0 can stick to BIOS-scheme or a new pirq namespace scheme
        - Dom0 can also decide the scheme of domU by pciback

So why not let dom0 to own allocation for pirq namespace of all domains?


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