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Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping
 CPUs
To:     Peter Zijlstra <peterz@infradead.org>,
        Marcelo Tosatti <mtosatti@redhat.com>
Cc:     linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
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        jesse.brandeburg@intel.com, lihong.yang@intel.com,
        helgaas@kernel.org, jeffrey.t.kirsher@intel.com,
        jacob.e.keller@intel.com, jlelli@redhat.com, hch@infradead.org,
        bhelgaas@google.com, mike.marciniszyn@intel.com,
        dennis.dalessandro@intel.com, thomas.lendacky@amd.com,
        jiri@nvidia.com, mingo@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, lgoncalv@redhat.com
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From:   Nitesh Narayan Lal <nitesh@redhat.com>
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Organization: Red Hat Inc,
Message-ID: <078e659e-d151-5bc2-a7dd-fe0070267cb3@redhat.com>
Date:   Tue, 20 Oct 2020 09:00:01 -0400
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On 10/20/20 3:30 AM, Peter Zijlstra wrote:
> 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.

Reading Marcelo's comment again I think what is really expected is 1
interrupt per non-isolated (housekeeping) CPU (not N interrupts).

My bad that I missed it initially.

--=20
Thanks
Nitesh


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