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

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Message-ID: <20210325173646.GG2356281@nvidia.com>
Date:   Thu, 25 Mar 2021 14:36:46 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Keith Busch <kbusch@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Leon Romanovsky <leon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leonro@...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 Thu, Mar 25, 2021 at 12:21:44PM -0500, Bjorn Helgaas wrote:

> NVMe and mlx5 have basically identical functionality in this respect.
> Other devices and vendors will likely implement similar functionality.
> It would be ideal if we had an interface generic enough to support
> them all.
> 
> Is the mlx5 interface proposed here sufficient to support the NVMe
> model?  I think it's close, but not quite, because the the NVMe
> "offline" state isn't explicitly visible in the mlx5 model.

I thought Keith basically said "offline" wasn't really useful as a
distinct idea. It is an artifact of nvme being a standards body
divorced from the operating system.

In linux offline and no driver attached are the same thing, you'd
never want an API to make a nvme device with a driver attached offline
because it would break the driver.

So I think it is good as is (well one of the 8 versions anyhow).

Keith didn't go into detail why the queue allocations in nvme were any
different than the queue allocations in mlx5. I expect they can
probably work the same where the # of interrupts is an upper bound on
the # of CPUs that can get queues and the device, once instantiated,
could be configured for the number of queues to actually operate, if
it wants.

Jason