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

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Date:   Sun, 18 Sep 2016 18:46:39 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>
CC:     iovisor-dev <iovisor-dev@...ts.iovisor.org>,
        <netdev@...r.kernel.org>, 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

Hi Alexei,

On 07/09/2016 8:34 PM, Alexei Starovoitov wrote:
> 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.
Why do you expect an improvement in tcp_rr?
I don't see such in my tests.
>