netdev - Re: [PATCH bpf-next 1/3] xdp: Add bulk XDP

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Date:   Thu, 23 May 2019 13:11:20 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Cc:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        netdev@...r.kernel.org, xdp-newbies@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/3] xdp: Add bulk XDP_TX queue

Toshiaki Makita <makita.toshiaki@....ntt.co.jp> writes:

> XDP_TX is similar to XDP_REDIRECT as it essentially redirects packets to
> the device itself. XDP_REDIRECT has bulk transmit mechanism to avoid the
> heavy cost of indirect call but it also reduces lock acquisition on the
> destination device that needs locks like veth and tun.
>
> XDP_TX does not use indirect calls but drivers which require locks can
> benefit from the bulk transmit for XDP_TX as well.

XDP_TX happens on the same device, so there's an implicit bulking
happening because of the NAPI cycle. So why is an additional mechanism
needed (in the general case)?

-Toke