netdev - Re: [RFC PATCH 00/24] Introducing AF

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Date:   Wed, 7 Feb 2018 22:38:24 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        john fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Anjali Singhai Jain <anjali.singhai@...el.com>,
        "Shaw, Jeffrey B" <jeffrey.b.shaw@...el.com>,
        "Yigit, Ferruh" <ferruh.yigit@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [RFC PATCH 00/24] Introducing AF_XDP support

2018-02-07 18:59 GMT+01:00 Tom Herbert <tom@...bertland.com>:
> On Wed, Jan 31, 2018 at 5:53 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
[...]
>>
>> Below are the results in Mpps of the I40E NIC benchmark runs for 64
>> byte packets, generated by commercial packet generator HW that is
>> generating packets at full 40 Gbit/s line rate.
>>
>> XDP baseline numbers without this RFC:
>> xdp_rxq_info --action XDP_DROP 31.3 Mpps
>> xdp_rxq_info --action XDP_TX   16.7 Mpps
>>
>> XDP performance with this RFC i.e. with the buffer allocator:
>> XDP_DROP 21.0 Mpps
>> XDP_TX   11.9 Mpps
>>
>> AF_PACKET V4 performance from previous RFC on 4.14-rc7:
>> Benchmark   V2     V3     V4     V4+ZC
>> rxdrop      0.67   0.73   0.74   33.7
>> txpush      0.98   0.98   0.91   19.6
>> l2fwd       0.66   0.71   0.67   15.5
>>
>> AF_XDP performance:
>> Benchmark   XDP_SKB   XDP_DRV    XDP_DRV_ZC (all in Mpps)
>> rxdrop      3.3        11.6         16.9
>> txpush      2.2         NA*         21.8
>> l2fwd       1.7         NA*         10.4
>>
> Hi Bjorn,
>
> This is very impressive work, thank you for contributing it!
>

Thank you for looking at it! :-)

> For these benchmarks how are the AF_PACKET and AF_XDP numbers to be
> compared. For instance is rxdpop comparable to XDP_DROP and
> "xdp_rxq_info --action XDP_DROP"? Given your explanation below, I
> believe they are, but it might be better to make that clear up front.
>

Ah, yeah, that was a bit confusing:

"xdp_rxq_info --action XDP_DROP" is doing an XDP_DROP (no buffer
touching) and should be compared to "XDP_DROP". I meant to write
"xdp_rxq_info --action XDP_DROP" instead of "XDP_DROP" for the
second case.

So, what this shows is that the buffer allocation scheme in the patch
set (buff_pool) has a pretty hard performance regression (21.0 vs
31.3) on the regular XDP (and skb!) path. Not acceptable.

"rxdrop" from AF_PACKET V4 should be compared to "rxdrop" from
AF_XDP. This is dropping a packet in user space, whereas the former is
dropping a packet in XDP/kernel space.

Less confusing?


Björn