linux-kernel - RE: [RFC PATCH] irq/affinity: Mark the pre/post vectors as regular interrupts

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Date:   Thu, 20 Sep 2018 14:09:53 +0530
From:   Kashyap Desai <kashyap.desai@...adcom.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Dou Liyang <dou_liyang@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Shivasharan Srikanteshwara 
        <shivasharan.srikanteshwara@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>, ming.lei@...hat.com,
        Christoph Hellwig <hch@....de>, douly.fnst@...fujitsu.com,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: RE: [RFC PATCH] irq/affinity: Mark the pre/post vectors as regular interrupts

> This is the wrong direction as it does not allow to do initial affinity
> assignement for the non-managed interrupts on allocation time. And
that's
> what Kashyap and Sumit are looking for.
>
> The trivial fix for the possible breakage when irq_default_affinity !=
> cpu_possible_mask is to set the affinity for the pre/post vectors to
> cpu_possible_mask and be done with it.
>
> One other thing I noticed while staring at that is the fact, that the
PCI
> code does not care about the return value of irq_create_affinity_masks()
at
> all. It just proceeds if masks is NULL as if the stuff was requested
with
> the affinity descriptor pointer being NULL. I don't think that's a
> brilliant idea because the drivers might rely on the interrupt being
> managed, but it might be a non-issue and just result in bad locality.
>
> Christoph?
>
> So back to the problem at hand. We need to change the affinity
management
> scheme in a way which lets us differentiate between managed and
> unmanaged
> interrupts, so it allows to automatically assign (initial) affinity to
all
> of them.
>
> Right now everything is bound to the cpumasks array, which does not
allow
> to convey more information. So we need to come up with something
> different.
>
> Something like the below (does not compile and is just for reference)
> should do the trick. I'm not sure whether we want to convey the
information
> (masks and bitmap) in a single data structure or not, but that's an
> implementation detail.


Dou -  Do you want me to test your patch or shall I wait for next version
?

>
> Thanks,
>
> 	tglx
>
> 8<---------
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -535,15 +535,16 @@ static struct msi_desc *
>  msi_setup_entry(struct pci_dev *dev, int nvec, const struct
irq_affinity *affd)
>  {
>  	struct cpumask *masks = NULL;
> +	unsigned long managed = 0;
>  	struct msi_desc *entry;
>  	u16 control;
>
>  	if (affd)
> -		masks = irq_create_affinity_masks(nvec, affd);
> +		masks = irq_create_affinity_masks(nvec, affd, &managed);
>
>
>  	/* MSI Entry Initialization */
> -	entry = alloc_msi_entry(&dev->dev, nvec, masks);
> +	entry = alloc_msi_entry(&dev->dev, nvec, masks, managed);
>  	if (!entry)
>  		goto out;
>
> @@ -672,15 +673,22 @@ static int msix_setup_entries(struct pci
>  			      struct msix_entry *entries, int nvec,
>  			      const struct irq_affinity *affd)
>  {
> +	/*
> +	 * MSIX_MAX_VECTORS = 2048, i.e. 256 bytes. Might need runtime
> +	 * allocation. OTOH, are 2048 vectors realistic?
> +	 */
> +	DECLARE_BITMAP(managed, MSIX_MAX_VECTORS);
>  	struct cpumask *curmsk, *masks = NULL;
>  	struct msi_desc *entry;
>  	int ret, i;
>
>  	if (affd)
> -		masks = irq_create_affinity_masks(nvec, affd);
> +		masks = irq_create_affinity_masks(nvec, affd, managed);
>
>  	for (i = 0, curmsk = masks; i < nvec; i++) {
> -		entry = alloc_msi_entry(&dev->dev, 1, curmsk);
> +		unsigned long m = test_bit(i, managed) ? 1 : 0;
> +
> +		entry = alloc_msi_entry(&dev->dev, 1, curmsk, m);
>  		if (!entry) {
>  			if (!i)
>  				iounmap(base);
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -27,7 +27,8 @@
>   * and the affinity masks from @affinity are copied.
>   */
>  struct msi_desc *
> -alloc_msi_entry(struct device *dev, int nvec, const struct cpumask
*affinity)
> +alloc_msi_entry(struct device *dev, int nvec, const struct cpumask
*affinity,
> +		unsigned long managed)
>  {
>  	struct msi_desc *desc;
>
> @@ -38,6 +39,7 @@ alloc_msi_entry(struct device *dev, int
>  	INIT_LIST_HEAD(&desc->list);
>  	desc->dev = dev;
>  	desc->nvec_used = nvec;
> +	desc->managed = managed;
>  	if (affinity) {
>  		desc->affinity = kmemdup(affinity,
>  			nvec * sizeof(*desc->affinity), GFP_KERNEL);
> @@ -416,7 +418,7 @@ int msi_domain_alloc_irqs(struct irq_dom
>
>  		virq = __irq_domain_alloc_irqs(domain, -1,
desc->nvec_used,
>  					       dev_to_node(dev), &arg,
false,
> -					       desc->affinity);
> +					       desc->affinity,
desc->managed);
>  		if (virq < 0) {
>  			ret = -ENOSPC;
>  			if (ops->handle_error)