netdev - Re: [PATCH RFC 04/11] net/mlx5e: Build RX SKB on demand

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Date:   Wed, 7 Sep 2016 10:34:51 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     iovisor-dev <iovisor-dev@...ts.iovisor.org>,
        netdev@...r.kernel.org, Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.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>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH RFC 04/11] net/mlx5e: Build RX SKB on demand

On Wed, Sep 07, 2016 at 03:42:25PM +0300, Saeed Mahameed wrote:
> For non-striding RQ configuration before this patch we had a ring
> with pre-allocated SKBs and mapped the SKB->data buffers for
> device.
> 
> For robustness and better RX data buffers management, we allocate a
> page per packet and build_skb around it.
> 
> This patch (which is a prerequisite for XDP) will actually reduce
> performance for normal stack usage, because we are now hitting a bottleneck
> in the page allocator. A later patch of page reuse mechanism will be
> needed to restore or even improve performance in comparison to the old
> RX scheme.
> 
> Packet rate performance testing was done with pktgen 64B packets on xmit
> side and TC drop action on RX side.
> 
> CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
> 
> Comparison is done between:
>  1.Baseline, before 'net/mlx5e: Build RX SKB on demand'
>  2.Build SKB with RX page cache (This patch)
> 
> Streams    Baseline    Build SKB+page-cache    Improvement
> -----------------------------------------------------------
> 1          4.33Mpps      5.51Mpps                27%
> 2          7.35Mpps      11.5Mpps                52%
> 4          14.0Mpps      16.3Mpps                16%
> 8          22.2Mpps      29.6Mpps                20%
> 16         24.8Mpps      34.0Mpps                17%

Impressive gains for build_skb. I think it should help ip forwarding too
and likely tcp_rr. tcp_stream shouldn't see any difference.
If you can benchmark that along with pktgen+tc_drop it would
help to better understand the impact of the changes.