netdev - Re: [PATCH mlx5-next v7 0/4] Dynamically assign MSI-X vectors count

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Date:   Fri, 26 Mar 2021 16:01:48 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Leon Romanovsky <leon@...nel.org>,
        Keith Busch <kbusch@...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>,
        "David S . Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH mlx5-next v7 0/4] Dynamically assign MSI-X vectors count

On Fri, Mar 26, 2021 at 11:50:44AM -0700, Alexander Duyck wrote:

> My concern would be that we are defining the user space interface.
> Once we have this working as a single operation I could see us having
> to support it that way going forward as somebody will script something
> not expecting an "offline" sysfs file, and the complaint would be that
> we are breaking userspace if we require the use of an "offline"
> file.

Well, we wouldn't do that. The semantic we define here is that the
msix_count interface 'auto-offlines' if that is what is required. If
we add some formal offline someday then 'auto-offline' would be a NOP
when the device is offline and do the same online/offline sequence as
today if it isn't.

> I almost wonder if it wouldn't make sense to just partition this up to
> handle flexible resources in the future. Maybe something like having
> the directory setup such that you have "sriov_resources/msix/" and

This is supposed to be about PCI properties, that is why we are doing
it in the PCI layer.

If you want to see something that handles non-PCI properties too then
Leon needs to make the whole thing general so the device driver can
give a list of properties it wants to configure and the core manages
the thing.

But at that point, why involve the PCI core in the first place? Just
put the complex configuration in the driver, use configfs or devlink
or nvmecli or whatever is appropriate.

And we are doing that too, there will also be pre-driver configuration
in devlink for *non PCI* properties. *shrug*

Jason