netdev - Re: [PATCH bpf-next v4 05/17] xsk: Change the default frame size to 4096 and allow controlling it

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Message-ID: <20190612131017.766b4e82@cakuba.netronome.com>
Date:   Wed, 12 Jun 2019 13:10:17 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jonathan Lemon <bsd@...com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Maciej Fijalkowski <maciejromanfijalkowski@...il.com>
Subject: Re: [PATCH bpf-next v4 05/17] xsk: Change the default frame size to
 4096 and allow controlling it

On Wed, 12 Jun 2019 15:56:43 +0000, Maxim Mikityanskiy wrote:
> The typical XDP memory scheme is one packet per page. Change the AF_XDP
> frame size in libbpf to 4096, which is the page size on x86, to allow
> libbpf to be used with the drivers with the packet-per-page scheme.

This is slightly surprising.  Why does the driver care about the bufsz?

You're not supposed to so page operations on UMEM pages, anyway.
And the RX size filter should be configured according to MTU regardless
of XDP state.

Can you explain?

> Add a command line option -f to xdpsock to allow to specify a custom
> frame size.
> 
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> Reviewed-by: Tariq Toukan <tariqt@...lanox.com>
> Acked-by: Saeed Mahameed <saeedm@...lanox.com>