linux-kernel - Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq

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Message-ID: <20201020073055.GY2611@hirez.programming.kicks-ass.net>
Date:   Tue, 20 Oct 2020 09:30:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        frederic@...nel.org, sassmann@...hat.com,
        jesse.brandeburg@...el.com, lihong.yang@...el.com,
        helgaas@...nel.org, jeffrey.t.kirsher@...el.com,
        jacob.e.keller@...el.com, jlelli@...hat.com, hch@...radead.org,
        bhelgaas@...gle.com, mike.marciniszyn@...el.com,
        dennis.dalessandro@...el.com, thomas.lendacky@....com,
        jiri@...dia.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, lgoncalv@...hat.com
Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to
 housekeeping CPUs

On Mon, Oct 19, 2020 at 11:00:05AM -0300, Marcelo Tosatti wrote:
> > So I think it is important to figure out what that driver really wants
> > in the nohz_full case. If it wants to retain N interrupts per CPU, and
> > only reduce the number of CPUs, the proposed interface is wrong.
> 
> It wants N interrupts per non-isolated (AKA housekeeping) CPU.

Then the patch is wrong and the interface needs changing from @min_vecs,
@max_vecs to something that expresses the N*nr_cpus relation.