linux-kernel - Re: [PATCH v6 01/29] irq/matrix: Expose functions to allocate the best CPU for new vectors

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Message-ID: <878rreh27n.ffs@tglx>
Date:   Fri, 06 May 2022 21:48:28 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        x86@...nel.org
Cc:     Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v6 01/29] irq/matrix: Expose functions to allocate the
 best CPU for new vectors

Ricardo,

On Thu, May 05 2022 at 16:59, Ricardo Neri wrote:
> Certain types of interrupts, such as NMI, do not have an associated vector.
> They, however, target specific CPUs. Thus, when assigning the destination
> CPU, it is beneficial to select the one with the lowest number of
> vectors.

Why is that beneficial especially in the context of a NMI watchdog which
then broadcasts the NMI to all other CPUs?

That's wishful thinking perhaps, but I don't see any benefit at all.

> Prepend the functions matrix_find_best_cpu_managed() and
> matrix_find_best_cpu_managed()

The same function prepended twice becomes two functions :)

> with the irq_ prefix and expose them for
> IRQ controllers to use when allocating and activating vector-less IRQs.

There is no such thing like a vectorless IRQ. NMIs have a vector. Can we
please describe facts and not pulled out of thin air concepts which do
not exist?

Thanks,

        tglx