[PATCH V2 1/3] PCI/MSI: preference to returning -ENOSPC from pci_alloc_irq_vectors_affinity
From: helgaas@kernel.org (Bjorn Helgaas)
Date: 2018-12-31 22:00:59
Also in:
linux-pci
On Sat, Dec 29, 2018@11:26:48AM +0800, Ming Lei wrote:
The API of pci_alloc_irq_vectors_affinity() requires to return -ENOSPC if leass than @min_vecs interrupt vectors are available for @dev.
s/leass/fewer/
However, this way may be changed by falling back to __pci_enable_msi_range(), for example, if the device isn't capable of MSI, __pci_enable_msi_range() will return -EINVAL, and finally it is returned to users of pci_alloc_irq_vectors_affinity() even though there are quite MSIX vectors available. This way violates the interface.
I *think* the above means: If a device supports MSI-X but not MSI and a caller requests @min_vecs that can't be satisfied by MSI-X, we previously returned -EINVAL (from the failed attempt to enable MSI), not -ENOSPC. and I agree that this doesn't match the documented API.
Users of pci_alloc_irq_vectors_affinity() may try to reduce irq vectors and allocate vectors again in case that -ENOSPC is returned, such as NVMe, so we need to respect the current interface and give preference to -ENOSPC.
I thought the whole point of the (min_vecs, max_vecs) tuple was to avoid this sort of "reduce and try again" iteration in the callers.
quoted hunk ↗ jump to hunk
Cc: Jens Axboe <axboe at fb.com>, Cc: Keith Busch <keith.busch at intel.com>, Cc: linux-pci at vger.kernel.org, Cc: Bjorn Helgaas <bhelgaas at google.com>, Signed-off-by: Ming Lei <ming.lei at redhat.com> --- drivers/pci/msi.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-)diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c index 7a1c8a09efa5..91b4f03fee91 100644 --- a/drivers/pci/msi.c +++ b/drivers/pci/msi.c@@ -1168,7 +1168,8 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs, const struct irq_affinity *affd) { static const struct irq_affinity msi_default_affd; - int vecs = -ENOSPC; + int msix_vecs = -ENOSPC; + int msi_vecs = -ENOSPC; if (flags & PCI_IRQ_AFFINITY) { if (!affd)@@ -1179,16 +1180,17 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs, } if (flags & PCI_IRQ_MSIX) { - vecs = __pci_enable_msix_range(dev, NULL, min_vecs, max_vecs, - affd); - if (vecs > 0) - return vecs; + msix_vecs = __pci_enable_msix_range(dev, NULL, min_vecs, + max_vecs, affd); + if (msix_vecs > 0) + return msix_vecs; } if (flags & PCI_IRQ_MSI) { - vecs = __pci_enable_msi_range(dev, min_vecs, max_vecs, affd); - if (vecs > 0) - return vecs; + msi_vecs = __pci_enable_msi_range(dev, min_vecs, max_vecs, + affd); + if (msi_vecs > 0) + return msi_vecs; } /* use legacy irq if allowed */@@ -1199,7 +1201,7 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs, } } - return vecs; + return msix_vecs == -ENOSPC ? msix_vecs : msi_vecs;
If you know you want to return -ENOSPC, just return that, not a
variable that happens to contain it, i.e.,
if (msix_vecs == -ENOSPC)
return -ENOSPC;
return msi_vecs;
} EXPORT_SYMBOL(pci_alloc_irq_vectors_affinity); -- 2.9.5 _______________________________________________ Linux-nvme mailing list Linux-nvme at lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme