netdev - RE: [PATCH bpf-next v2 2/2] xdp: Use bulking for non-map XDP

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Message-ID: <5e1f6b61c9d74_72f02acbae15e5c460@john-XPS-13-9370.notmuch>
Date:   Wed, 15 Jan 2020 11:43:29 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: RE: [PATCH bpf-next v2 2/2] xdp: Use bulking for non-map XDP_REDIRECT
 and consolidate code paths

Toke Høiland-Jørgensen wrote:
> From: Toke Høiland-Jørgensen <toke@...hat.com>
> 
> Since the bulk queue used by XDP_REDIRECT now lives in struct net_device,
> we can re-use the bulking for the non-map version of the bpf_redirect()
> helper. This is a simple matter of having xdp_do_redirect_slow() queue the
> frame on the bulk queue instead of sending it out with __bpf_tx_xdp().
> 
> Unfortunately we can't make the bpf_redirect() helper return an error if
> the ifindex doesn't exit (as bpf_redirect_map() does), because we don't
> have a reference to the network namespace of the ingress device at the time
> the helper is called. So we have to leave it as-is and keep the device
> lookup in xdp_do_redirect_slow().
> 
> Since this leaves less reason to have the non-map redirect code in a
> separate function, so we get rid of the xdp_do_redirect_slow() function
> entirely. This does lose us the tracepoint disambiguation, but fortunately
> the xdp_redirect and xdp_redirect_map tracepoints use the same tracepoint
> entry structures. This means both can contain a map index, so we can just
> amend the tracepoint definitions so we always emit the xdp_redirect(_err)
> tracepoints, but with the map ID only populated if a map is present. This
> means we retire the xdp_redirect_map(_err) tracepoints entirely, but keep
> the definitions around in case someone is still listening for them.
> 
> With this change, the performance of the xdp_redirect sample program goes
> from 5Mpps to 8.4Mpps (a 68% increase).
> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>

Acked-by: John Fastabend <john.fastabend@...il.com>