netdev - Re: [PATCH RFC 08/11] net/mlx5e: XDP fast RX drop bpf programs support

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Date:   Thu, 8 Sep 2016 06:58:46 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        iovisor-dev <iovisor-dev@...ts.iovisor.org>
Cc:     netdev@...r.kernel.org, Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Martin KaFai Lau <kafai@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Rana Shahout <ranas@...lanox.com>
Subject: Re: [PATCH RFC 08/11] net/mlx5e: XDP fast RX drop bpf programs
 support


On 16-09-07 08:42 AM, Saeed Mahameed wrote:

> Comparison is done between:
> 	1. Baseline, Before this patch with TC drop action
> 	2. This patch with TC drop action
> 	3. This patch with XDP RX fast drop
>
> Streams    Baseline(TC drop)    TC drop    XDP fast Drop
> --------------------------------------------------------------
> 1           5.51Mpps            5.14Mpps     13.5Mpps
> 2           11.5Mpps            10.0Mpps     25.1Mpps
> 4           16.3Mpps            17.2Mpps     35.4Mpps
> 8           29.6Mpps            28.2Mpps     45.8Mpps*
> 16          34.0Mpps            30.1Mpps     45.8Mpps*
>
> It seems that there is around ~5% degradation between Baseline
> and this patch with single stream when comparing packet rate with TC drop,
> it might be related to XDP code overhead or new cache misses added by
> XDP code.


I would suspect this degradation would affect every other packet that
has no interest in XDP.
if you were trying to test forwarding, adding a tc action to
accept and count packets will be sufficient. Since you are not:

Try to baseline sending the wrong destination MAC  address (i.e one
not understood by host). The kernel will eventually drop it
somewhere pre-IP processing time (and you can see difference with
XDP compiled in).

Slightly tangent question: Would it be fair to assume that this
hardware can drop at wire rate if you instead used an offloaded
tc rule?

cheers,
jamal