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

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Message-ID: <20200929174654.GA773@infradead.org>
Date:   Tue, 29 Sep 2020 18:46:54 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>, hch@...radead.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        frederic@...nel.org, mtosatti@...hat.com, sassmann@...hat.com,
        jesse.brandeburg@...el.com, lihong.yang@...el.com,
        jeffrey.t.kirsher@...el.com, jacob.e.keller@...el.com,
        jlelli@...hat.com, bhelgaas@...gle.com, mike.marciniszyn@...el.com,
        dennis.dalessandro@...el.com, thomas.lendacky@....com,
        jiri@...dia.com, mingo@...hat.com, peterz@...radead.org,
        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, Sep 28, 2020 at 04:59:31PM -0500, Bjorn Helgaas wrote:
> [to: Christoph in case he has comments, since I think he wrote this code]

I think I actually suggested this a few iterations back.

> > +	hk_cpus = housekeeping_num_online_cpus(HK_FLAG_MANAGED_IRQ);
> > +
> > +	/*
> > +	 * If we have isolated CPUs for use by real-time tasks, to keep the
> > +	 * latency overhead to a minimum, device-specific IRQ vectors are moved
> > +	 * to the housekeeping CPUs from the userspace by changing their
> > +	 * affinity mask. Limit the vector usage to keep housekeeping CPUs from
> > +	 * running out of IRQ vectors.
> > +	 */
> > +	if (hk_cpus < num_online_cpus()) {

I woukd have moved the assignment to hk_cpus below the comment and
just above the if, but that is really just a minor style preference.

Otherwise this looks good:

Acked-by: Christoph Hellwig <hch@....de>