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Re: [PATCH v2 5/6] x86/irq: print nr_irqs as limit on the number of MSI(-X) interrupts
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 5 Jul 2022 16:15:57 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 05 Jul 2022 14:16:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.06.2022 10:54, Roger Pau Monne wrote:
> Using nr_irqs minus nr_irqs_gsi is misleading, as GSI interrupts are
> not allocated unless requested by the hardware domain, so a hardware
> domain could not use any GSI (or just one for the ACPI SCI), and hence
> (almost) all nr_irqs will be available for MSI(-X) usage.
Looking at create_irq() I find a loop going from nr_irqs_gsi to nr_irqs.
Similar in get_free_pirq(). All lower numbers aren't eligible for use by
MSI/MSI-X. We can't allow the lower ones to be used for other than GSI
purposes because we can't know whether any device will become enabled
(perhaps long after boot) which wants to use a specific GSI.
Jan
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