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SubjectRe: [PATCH 08/13] pci: spread interrupt vectors in pci_alloc_irq_vectors
On Mon, Jul 04, 2016 at 05:39:29PM +0900, Christoph Hellwig wrote:
> Set the affinity_mask in the PCI device before allocating vectors so that
> the affinity can be propagated through the MSI descriptor structures to
> the core IRQ code. Add a new helper __pci_enable_msi_range which is
> similar to __pci_enable_msix_range introduced in the last patch so that
> we can allocate the affinity mask in a self-contained fashion and for the
> right number of vectors.
>
> A new PCI_IRQ_NOAFFINITY flag is added to pci_alloc_irq_vectors so that
> this function can also be used by drivers that don't wish to use the
> automatic affinity assignment.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> Documentation/PCI/MSI-HOWTO.txt | 3 +-
> drivers/pci/msi.c | 72 ++++++++++++++++++++++++++++++++++++++---
> include/linux/pci.h | 2 ++
> 3 files changed, 72 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
> index 35d1326..dcd3f6d 100644
> --- a/Documentation/PCI/MSI-HOWTO.txt
> +++ b/Documentation/PCI/MSI-HOWTO.txt
> @@ -95,7 +95,8 @@ argument set to this limit, and the PCI core will return -ENOSPC if it can't
> meet the minimum number of vectors.
> The flags argument should normally be set to 0, but can be used to
> pass the PCI_IRQ_NOMSI and PCI_IRQ_NOMSIX flag in case a device claims
> -to support MSI or MSI-X, but the support is broken.
> +to support MSI or MSI-X, but the support is broken, or to PCI_IRQ_NOAFFINITY
> +if the driver does not wish to use the automatic affinity assignment feature.
>
> To get the Linux IRQ numbers passed to request_irq and free_irq
> and the vectors use the following function:
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index 6b0834d..7f38e07 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -568,6 +568,7 @@ static struct msi_desc *msi_setup_entry(struct pci_dev *dev, int nvec)
> entry->msi_attrib.multi_cap = (control & PCI_MSI_FLAGS_QMASK) >> 1;
> entry->msi_attrib.multiple = ilog2(__roundup_pow_of_two(nvec));
> entry->nvec_used = nvec;
> + entry->affinity = dev->irq_affinity;

irq_create_affinity_mask() bails out with no affinity in case of single
vector, but alloc_descs() (see below (*)) assigns the whole affinity
mask. It should be consistent instead.

Actually, I just realized pci_alloc_irq_vectors() should probably call
irq_create_affinity_mask() and handle it in a consistent way for all four
cases: MSI-X, mulit-MSI, MSI and legacy.

Optionally, the three latter could be dropped for now so you could proceed
with NVMe.

> if (control & PCI_MSI_FLAGS_64BIT)
> entry->mask_pos = dev->msi_cap + PCI_MSI_MASK_64;
> @@ -679,10 +680,18 @@ static void __iomem *msix_map_region(struct pci_dev *dev, unsigned nr_entries)
> static int msix_setup_entries(struct pci_dev *dev, void __iomem *base,
> struct msix_entry *entries, int nvec)
> {
> + const struct cpumask *mask = NULL;
> struct msi_desc *entry;
> - int i;
> + int cpu = -1, i;
>
> for (i = 0; i < nvec; i++) {
> + if (dev->irq_affinity) {
> + cpu = cpumask_next(cpu, dev->irq_affinity);
> + if (cpu >= nr_cpu_ids)
> + cpu = cpumask_first(dev->irq_affinity);
> + mask = cpumask_of(cpu);
> + }
> +

(*) In the future IRQ vs CPU mapping 1:N is possible/desirable so I suppose
this piece of code worth a comment or better - a separate function. In fact,
this algorithm already exists in alloc_descs(), which makes even more sense
to factor it out:

for (i = 0; i < cnt; i++) {
if (affinity) {
cpu = cpumask_next(cpu, affinity);
if (cpu >= nr_cpu_ids)
cpu = cpumask_first(affinity);
node = cpu_to_node(cpu);

/*
* For single allocations we use the caller provided
* mask otherwise we use the mask of the target cpu
*/
mask = cnt == 1 ? affinity : cpumask_of(cpu);
}

[...]

}

> entry = alloc_msi_entry(&dev->dev);
> if (!entry) {
> if (!i)
> @@ -699,6 +708,7 @@ static int msix_setup_entries(struct pci_dev *dev, void __iomem *base,
> entry->msi_attrib.default_irq = dev->irq;
> entry->mask_base = base;
> entry->nvec_used = 1;
> + entry->affinity = mask;
>
> list_add_tail(&entry->list, dev_to_msi_list(&dev->dev));
> }
> @@ -1121,8 +1131,53 @@ int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
> }
> EXPORT_SYMBOL(pci_enable_msix_range);
>
> +static int __pci_enable_msi_range(struct pci_dev *dev, int min_vecs, int max_vecs,

So I won't comment on this function before the above is decided.

> + unsigned int flags)
> +{
> + int vecs, ret;
> +
> + if (!pci_msi_supported(dev, min_vecs))
> + return -EINVAL;
> +
> + vecs = pci_msi_vec_count(dev);
> + if (vecs < 0)
> + return vecs;
> + if (vecs < min_vecs)
> + return -EINVAL;
> + if (vecs > max_vecs)
> + vecs = max_vecs;
> +
> +retry:
> + if (vecs < min_vecs)
> + return -ENOSPC;
> +
> + if (!(flags & PCI_IRQ_NOAFFINITY)) {
> + dev->irq_affinity = irq_create_affinity_mask(&vecs);
> + if (vecs < min_vecs) {
> + ret = -ERANGE;
> + goto out_fail;
> + }
> + }
> +
> + ret = msi_capability_init(dev, vecs);
> + if (ret)
> + goto out_fail;
> +
> + return vecs;
> +
> +out_fail:
> + kfree(dev->irq_affinity);
> + if (ret >= 0) {
> + /* retry with the actually supported number of vectors */
> + vecs = ret;
> + goto retry;
> + }
> +
> + return ret;
> +}
> +
> static int __pci_enable_msix_range(struct pci_dev *dev, unsigned int min_vecs,
> - unsigned int max_vecs)
> + unsigned int max_vecs, unsigned int flags)
> {
> int vecs = max_vecs, ret, i;
>
> @@ -1138,6 +1193,13 @@ retry:
> for (i = 0; i < vecs; i++)
> dev->msix_vectors[i].entry = i;
>
> + if (!(flags & PCI_IRQ_NOAFFINITY)) {
> + dev->irq_affinity = irq_create_affinity_mask(&vecs);
> + ret = -ENOSPC;
> + if (vecs < min_vecs)
> + goto out_fail;
> + }
> +
> ret = pci_enable_msix(dev, dev->msix_vectors, vecs);
> if (ret)
> goto out_fail;
> @@ -1147,6 +1209,8 @@ retry:
> out_fail:
> kfree(dev->msix_vectors);
> dev->msix_vectors = NULL;
> + kfree(dev->irq_affinity);
> + dev->irq_affinity = NULL;
>
> if (ret >= 0) {
> /* retry with the actually supported number of vectors */
> @@ -1180,13 +1244,13 @@ int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> int vecs;
>
> if (!(flags & PCI_IRQ_NOMSIX)) {
> - vecs = __pci_enable_msix_range(dev, min_vecs, max_vecs);
> + vecs = __pci_enable_msix_range(dev, min_vecs, max_vecs, flags);
> if (vecs > 0)
> return vecs;
> }
>
> if (!(flags & PCI_IRQ_NOMSI)) {
> - vecs = pci_enable_msi_range(dev, min_vecs, max_vecs);
> + vecs = __pci_enable_msi_range(dev, min_vecs, max_vecs, flags);
> if (vecs > 0)
> return vecs;
> }
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 129871f..6a64c54 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -321,6 +321,7 @@ struct pci_dev {
> */
> unsigned int irq;
> struct msix_entry *msix_vectors;
> + struct cpumask *irq_affinity;
> struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */
>
> bool match_driver; /* Skip attaching driver */
> @@ -1240,6 +1241,7 @@ int pci_set_vga_state(struct pci_dev *pdev, bool decode,
>
> #define PCI_IRQ_NOMSI (1 << 0) /* don't try to use MSI interrupts */
> #define PCI_IRQ_NOMSIX (1 << 1) /* don't try to use MSI-X interrupts */
> +#define PCI_IRQ_NOAFFINITY (1 << 2) /* don't auto-assign affinity */
>
> /* kmem_cache style wrapper around pci_alloc_consistent() */
>
> --
> 2.1.4
>

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