Re: [PATCH v3 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs

[Nitesh Narayan Lal]

On 9/25/20 5:38 PM, Nitesh Narayan Lal wrote:
> On 9/25/20 4:23 PM, Bjorn Helgaas wrote:

[...]

>>> +	/*
>>> +	 * 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()) {
>>> +		if (hk_cpus < min_vecs)
>>> +			max_vecs = min_vecs;
>>> +		else if (hk_cpus < max_vecs)
>>> +			max_vecs = hk_cpus;
>>> +	}
>> It seems like you'd want to do this inside
>> pci_alloc_irq_vectors_affinity() since that's an exported interface,
>> and drivers that use it will bypass the limiting you're doing here.
> Good point, few drivers directly use this.
> I took a quick look and it seems I may also have to take the pre and the
> post vectors into consideration.
>

It seems my initial interpretation was incorrect, reserved vecs (pre+post)
should always be less than the min_vecs.
So, FWIU we should be fine in limiting the max_vecs.

I can make this change and do a repost.

Do you have any other concerns with this patch or with any of the other
patches?

[...]

-- 
Nitesh

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