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

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Date:   Mon, 25 Jan 2021 11:23:56 -0800
From:   Edwin Peer <edwin.peer@...adcom.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Parav Pandit <parav@...dia.com>, Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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 5:22 AM Jason Gunthorpe <jgg@...dia.com> wrote:

> SRIOV and SF's require a simple linear lookup to learn the "function"
> because the BAR space is required to be linear.

Isn't this still true even for NumVF's > 256? Wouldn't there still be
a contiguous VF BAR space? Don't the routing IDs simply carry on
incrementing by stride, with each being assigned the next slice of the
shared BAR space?

> Scaling a CAM to high sizes is physicaly infeasible, so all approaches
> to scaling PCI functions go this road of having a single large BAR
> space.

If the above is true, is there really a need to scale up CAM?

Regards,
Edwin Peer

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