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Re: [Xen-devel] [PATCH 0/4] xen: events: improve event channel IRQ alloc

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0/4] xen: events: improve event channel IRQ allocation strategy.
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Tue, 11 Jan 2011 13:34:59 -0500
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
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On Tue, Jan 11, 2011 at 05:19:49PM +0000, Ian Campbell wrote:
> The following series changes the Xen event channel infrastructure to
> make better use of the core IRQ allocation interfaces and simplifies
> our attempts to avoid clashes between GSIs and event channels.
> The two most interesting changes are:
>       * PV domU IRQ numbers are now completely dynamically allocated,
>         including those associated with PCI passthrough devices. Since
>         the guest sees no equivalent to GSI space there is no need to do
>         anything clever in this case like maintaining a 1-1 mapping
>         between GSI and IRQ. (this is impossible anyway since a PV guest
>         has no idea what the largest possible GSI is).
>       * PV dom0 and HVM guests now completely segregate GSIs from
>         dynamically allocated IRQs. In this case IRQs for GSIs are
>         allocated 1-1 beneath nr_irq_gsi (similar to native) and dynamic
>         IRQs (event channels, MSIs etc) are allocated above. This
>         simplifies the IRQ allocator code enormously.
> The series has been tested as:
>       * PV guest with a PCI passthrough device.

Which type of domain0? A 2.6.37 + Xen PCI backend + your patches?
Or the older 2.6.32?
>       * PV domain 0.
>       * HVM guest with and without XENFEAT_hvm_pirqs.
> It appears to do the correct thing in each case.

> I also tried HVM with PCI passthrough, which wasn't too successful due
> to my hardware not having an IOMMU, but it did appear to setup the IRQ
> mapping correctly at least.
> I don't intend this for 2.6.38 at this stage since it looks like:
>         67b0ea2bdcd7 xen/irq: Don't fall over when nr_irqs_gsi > nr_irqs.
>         d1b758ebc2a8 xen/irq: Cleanup the find_unbound_irq
> are sufficient (BTW this series follows those).
> Ian.
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