netdev - Re: [pull request][net-next V10 00/14] Add mlx5 subfunction support

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Message-ID: <CAKOOJTx7ogAvUkT5y8vKYp=KB+VSbe0MgXg5PuvjEiU_dO_5YA@mail.gmail.com>
Date:   Mon, 25 Jan 2021 11:34:49 -0800
From:   Edwin Peer <edwin.peer@...adcom.com>
To:     Parav Pandit <parav@...dia.com>
Cc:     Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        netdev <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        David Ahern <dsahern@...nel.org>,
        Kiran Patil <kiran.patil@...el.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        "Ertman, David M" <david.m.ertman@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [pull request][net-next V10 00/14] Add mlx5 subfunction support

On Mon, Jan 25, 2021 at 10:35 AM Edwin Peer <edwin.peer@...adcom.com> wrote:

> > Several weeks back, Jason already answered this VF scaling question from you at discussion [1].
> >
> > [1] https://lore.kernel.org/netdev/20201216023928.GG552508@nvidia.com/

Regarding these costs:

> A lot of the trappings that PCI-SIG requires to be implemented in HW
> for a VF, like PCI config space, MSI tables, BAR space, etc. is all
> just dead weight when scaling up to 1000's of VFs.

What do these amount to in practice? Presumably config space is backed
by normal memory controlled by firmware. Do VF's need to expose ECAM?
Also, don't MSI tables come out of the BAR budget? Is the required BAR
space necessarily more than any other addressable unit that can be
delegated to a SF?

Whatever the costs, presumably they need to be weighed against the
complexity costs of the alternative?

Regards,
Edwin Peer

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