Subject: Re: [PATCH mlx5-next v7 1/4] PCI: Add a sysfs file to change the MSI-X table size of SR-IOV VFs

From: Leon Romanovsky <[email-masked]>
Date: Mon, 1 Mar 2021 10:53:39 +0200

On Mon, Mar 01, 2021 at 09:37:17AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Mar 01, 2021 at 10:32:09AM +0200, Leon Romanovsky wrote:
> > On Mon, Mar 01, 2021 at 09:14:42AM +0100, Greg Kroah-Hartman wrote:
> > > On Mon, Mar 01, 2021 at 09:55:21AM +0200, Leon Romanovsky wrote:
> > > > From: Leon Romanovsky <[email-masked]>
> > > >
> > > > A typical cloud provider SR-IOV use case is to create many VFs for use by
> > > > guest VMs. The VFs may not be assigned to a VM until a customer requests a
> > > > VM of a certain size, e.g., number of CPUs. A VF may need MSI-X vectors
> > > > proportional to the number of CPUs in the VM, but there is no standard way
> > > > to change the number of MSI-X vectors supported by a VF.
> > > >
> > > > Some Mellanox ConnectX devices support dynamic assignment of MSI-X vectors
> > > > to SR-IOV VFs. This can be done by the PF driver after VFs are enabled,
> > > > and it can be done without affecting VFs that are already in use. The
> > > > hardware supports a limited pool of MSI-X vectors that can be assigned to
> > > > the PF or to individual VFs.  This is device-specific behavior that
> > > > requires support in the PF driver.
> > > >
> > > > Add a read-only "sriov_vf_total_msix" sysfs file for the PF and a writable
> > > > "sriov_vf_msix_count" file for each VF. Management software may use these
> > > > to learn how many MSI-X vectors are available and to dynamically assign
> > > > them to VFs before the VFs are passed through to a VM.
> > > >
> > > > If the PF driver implements the ->sriov_get_vf_total_msix() callback,
> > > > "sriov_vf_total_msix" contains the total number of MSI-X vectors available
> > > > for distribution among VFs.
> > > >
> > > > If no driver is bound to the VF, writing "N" to "sriov_vf_msix_count" uses
> > > > the PF driver ->sriov_set_msix_vec_count() callback to assign "N" MSI-X
> > > > vectors to the VF.  When a VF driver subsequently reads the MSI-X Message
> > > > Control register, it will see the new Table Size "N".
> > > >
> > > > Signed-off-by: Leon Romanovsky <[email-masked]>
> > > > ---
> > > >  Documentation/ABI/testing/sysfs-bus-pci |  29 +++++++
> > > >  drivers/pci/iov.c                       | 102 ++++++++++++++++++++++--
> > > >  drivers/pci/pci-sysfs.c                 |   3 +-
> > > >  drivers/pci/pci.h                       |   3 +-
> > > >  include/linux/pci.h                     |   8 ++
> > > >  5 files changed, 137 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> > > > index 25c9c39770c6..ebabd0d2ae88 100644
> > > > --- a/Documentation/ABI/testing/sysfs-bus-pci
> > > > +++ b/Documentation/ABI/testing/sysfs-bus-pci
> > > > @@ -375,3 +375,32 @@ Description:
> > > >  		The value comes from the PCI kernel device state and can be one
> > > >  		of: "unknown", "error", "D0", D1", "D2", "D3hot", "D3cold".
> > > >  		The file is read only.
> > > > +
> > > > +What:		/sys/bus/pci/devices/.../sriov_vf_total_msix
> > > > +Date:		January 2021
> > > > +Contact:	Leon Romanovsky <[email-masked]>
> > > > +Description:
> > > > +		This file is associated with a SR-IOV PF.  It contains the
> > > > +		total number of MSI-X vectors available for assignment to
> > > > +		all VFs associated with PF.  It will zero if the device
> > >
> > > "The value will be zero if the device..."
> >
> > Thanks, will fix when apply or resend if more fixes will be needed.
> >
> > >
> > > And definition of "VF" and PF" are where in this file?
> >
> > They come from the PCI spec. It is part of SR-IOV lingo.
>
> Yes, and the world does not have access to the PCI spec, so please
> provide a hint as to what they are for those of us without access to
> such things.

No problem, I will replace PF to be "physical function" and VF to be
"virtual function".

Thanks

> thanks,
> greg k-h