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

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Message-ID: <87d0brxr9u.fsf@toke.dk>
Date:   Fri, 10 Jan 2020 16:30:53 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>, bpf <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>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH bpf-next 2/2] xdp: Use bulking for non-map XDP_REDIRECT

Björn Töpel <bjorn.topel@...il.com> writes:

> On Fri, 10 Jan 2020 at 15:22, Toke Høiland-Jørgensen <toke@...hat.com> 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().
>>
>> With this change, the performance of the xdp_redirect sample program goes
>> from 5Mpps to 8.4Mpps (a 68% increase).
>>
>
> After these changes, does the noinline (commit 47b123ed9e99 ("xdp:
> split code for map vs non-map redirect")) still make sense?

Hmm, good question. The two code paths are certainly close to one
another; and I guess they could be consolidated further.

The best case would be if we had a way to lookup the ifindex directly in
the helper. Do you know if there's a way to get the current net
namespace from the helper? Can we use current->nsproxy->net_ns in that
context?

If we can, and if we don't mind merging the two different tracepoints,
the xdp_do_redirect() function could be made quite a bit leaner...

-Toke