On Sat, Jan 16, 2021 at 10:23:31AM +0200, Leon Romanovsky wrote:

On Thu, Jan 14, 2021 at 05:05:43PM -0700, Alex Williamson wrote:

quoted

On Thu, 14 Jan 2021 12:31:36 +0200
Leon Romanovsky [off-list ref] wrote:

quoted

From: Leon Romanovsky <leonro@nvidia.com>

Extend PCI sysfs interface with a new callback that allows configure
the number of MSI-X vectors for specific SR-IO VF. This is needed
to optimize the performance of newly bound devices by allocating
the number of vectors based on the administrator knowledge of targeted VM.

This function is applicable for SR-IOV VF because such devices allocate
their MSI-X table before they will run on the VMs and HW can't guess the
right number of vectors, so the HW allocates them statically and equally.

The newly added /sys/bus/pci/devices/.../sriov_vf_msix_count file will be seen
for the VFs and it is writable as long as a driver is not bounded to the VF.

The values accepted are:
 * > 0 - this will be number reported by the VF's MSI-X capability
 * < 0 - not valid
 * = 0 - will reset to the device default value

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 Documentation/ABI/testing/sysfs-bus-pci | 20 +++++++++
 drivers/pci/iov.c                       | 58 +++++++++++++++++++++++++
 drivers/pci/msi.c                       | 47 ++++++++++++++++++++
 drivers/pci/pci-sysfs.c                 |  1 +
 drivers/pci/pci.h                       |  2 +
 include/linux/pci.h                     |  3 ++
 6 files changed, 131 insertions(+)

<...>

quoted

quoted

+static umode_t sriov_vf_attrs_are_visible(struct kobject *kobj,
+					  struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+
+	if (dev_is_pf(dev))
+		return 0;

Wouldn't it be cleaner to also hide this on VFs where
pci_msix_vec_count() returns an error or where the PF driver doesn't
implement .sriov_set_msix_vec_count()?  IOW, expose it only where it
could actually work.

I wasn't sure about the policy in PCI/core, but sure will change.

I ended adding checks of msix_cap, but can't check .sriov_set_msix_vec_count.
The latter will require to hold device_lock on PF that can disappear later, it
is too racy.

Thanks