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SubjectRe: Affinity managed interrupts vs non-managed interrupts
Hello Sumit,

On Tue, Aug 28, 2018 at 12:04:52PM +0530, Sumit Saxena wrote:
> Affinity managed interrupts vs non-managed interrupts
>
> Hi Thomas,
>
> We are working on next generation MegaRAID product where requirement is- to
> allocate additional 16 MSI-x vectors in addition to number of MSI-x vectors
> megaraid_sas driver usually allocates. MegaRAID adapter supports 128 MSI-x
> vectors.
>
> To explain the requirement and solution, consider that we have 2 socket
> system (each socket having 36 logical CPUs). Current driver will allocate
> total 72 MSI-x vectors by calling API- pci_alloc_irq_vectors(with flag-
> PCI_IRQ_AFFINITY). All 72 MSI-x vectors will have affinity across NUMA node
> s and interrupts are affinity managed.
>
> If driver calls- pci_alloc_irq_vectors_affinity() with pre_vectors = 16
> and, driver can allocate 16 + 72 MSI-x vectors.

Could you explain a bit what the specific use case the extra 16 vectors
is?

>
> All pre_vectors (16) will be mapped to all available online CPUs but e
> ffective affinity of each vector is to CPU 0. Our requirement is to have pre
> _vectors 16 reply queues to be mapped to local NUMA node with
> effective CPU should
> be spread within local node cpu mask. Without changing kernel code, we can

If all CPUs in one NUMA node is offline, can this use case work as expected?
Seems we have to understand what the use case is and how it works.


Thanks,
Ming

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