linux-kernel - Re: [Patch v1] i40e: limit the msix vectors based on housekeeping CPUs

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Date:   Fri, 26 Jun 2020 16:11:24 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, frederic@...nel.org,
        mtosatti@...hat.com, sassmann@...hat.com,
        jeffrey.t.kirsher@...el.com, jacob.e.keller@...el.com,
        jlelli@...hat.com
Subject: Re: [Patch v1] i40e: limit the msix vectors based on housekeeping
 CPUs


On 6/16/20 4:03 AM, Christoph Hellwig wrote:
> On Mon, Jun 15, 2020 at 04:21:25PM -0400, Nitesh Narayan Lal wrote:
>> +	hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ;
>> +	mask = housekeeping_cpumask(hk_flags);
>> +	cpus = cpumask_weight(mask);
> Code like this has no business inside a driver.  Please provide a
> proper core API for it instead.  Also please wire up
> pci_alloc_irq_vectors* to use this API as well.
>

Hi Christoph,

I have been looking into using nr_houskeeping_* API that I will be defining
within pci_alloc_irq_vectors* to limit the nr of vectors.
However, I am wondering about a few things:

- Some of the drivers such as i40e until now, use the num_online CPUs to
  restrict the number of vectors that they should create. Will it make sense if
  I restrict the maximum vectors requested based on
  nr_online/housekeeping_cpus (Though I will have to make sure that the
  min_vecs is always satisfied)?

  The other option would be to check for the total available vectors in all
  online/housekeeping CPUs for limiting the maxvecs, this way will probably be
  more accurate?

- Another thing that I am wondering about is the right way to test this change.

Please let me know if you have any suggestions?

-- 
Nitesh



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