netdev - Re: [PATCH bpf-next v6 07/12] net/mlx5e: Allow XSK frames smaller than a page

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Message-ID: <C5FEBF55-CC52-4489-955E-1202BB4FF193@gmail.com>
Date:   Fri, 30 Aug 2019 08:45:35 -0700
From:   "Jonathan Lemon" <jonathan.lemon@...il.com>
To:     "Kevin Laatz" <kevin.laatz@...el.com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        bjorn.topel@...el.com, magnus.karlsson@...el.com,
        jakub.kicinski@...ronome.com, saeedm@...lanox.com,
        maximmi@...lanox.com, stephen@...workplumber.org,
        bruce.richardson@...el.com, ciara.loftus@...el.com,
        bpf@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH bpf-next v6 07/12] net/mlx5e: Allow XSK frames smaller
 than a page



On 26 Aug 2019, at 19:25, Kevin Laatz wrote:

> From: Maxim Mikityanskiy <maximmi@...lanox.com>
>
> Relax the requirements to the XSK frame size to allow it to be smaller
> than a page and even not a power of two. The current implementation can
> work in this mode, both with Striding RQ and without it.
>
> The code that checks `mtu + headroom <= XSK frame size` is modified
> accordingly. Any frame size between 2048 and PAGE_SIZE is accepted.
>
> Functions that worked with pages only now work with XSK frames, even if
> their size is different from PAGE_SIZE.
>
> With XSK queues, regardless of the frame size, Striding RQ uses the
> stride size of PAGE_SIZE, and UMR MTTs are posted using starting
> addresses of frames, but PAGE_SIZE as page size. MTU guarantees that no
> packet data will overlap with other frames. UMR MTT size is made equal
> to the stride size of the RQ, because UMEM frames may come in random
> order, and we need to handle them one by one. PAGE_SIZE is just a power
> of two that is bigger than any allowed XSK frame size, and also it
> doesn't require making additional changes to the code.
>
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> Reviewed-by: Saeed Mahameed <saeedm@...lanox.com>
Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>