netdev - Re: [PATCH mlx5-next v1 2/5] PCI: Add SR-IOV sysfs entry to read number of MSI-X vectors

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Date:   Thu, 14 Jan 2021 12:48:57 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
CC:     Leon Romanovsky <leon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, Netdev <netdev@...r.kernel.org>,
        Don Dutile <ddutile@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH mlx5-next v1 2/5] PCI: Add SR-IOV sysfs entry to read
 number of MSI-X vectors

On Thu, Jan 14, 2021 at 08:40:14AM -0800, Alexander Duyck wrote:

> Where I think you and I disagree is that I really think the MSI-X
> table size should be fixed at one value for the life of the VF.
> Instead of changing the table size it should be the number of vectors
> that are functional that should be the limit. Basically there should
> be only some that are functional and some that are essentially just
> dummy vectors that you can write values into that will never be used.

Ignoring the PCI config space to learn the # of available MSI-X
vectors is big break on the how the device's programming ABI works.

Or stated another way, that isn't compatible with any existing drivers
so it is basically not a useful approach as it can't be deployed.

I don't know why you think that is better.

Jason