netdev - Re: [PATCHv17 bpf-next 1/6] bpf: run devmap xdp_prog on flush instead of bulk enqueue

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Date:   Wed, 27 Jan 2021 16:58:10 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Toke Høiland-Jørgensen 
        <toke@...hat.com>, Jiri Benc <jbenc@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        brouer@...hat.com
Subject: Re: [PATCHv17 bpf-next 1/6] bpf: run devmap xdp_prog on flush
 instead of bulk enqueue

On Mon, 25 Jan 2021 20:45:11 +0800
Hangbin Liu <liuhangbin@...il.com> wrote:

> By using xdp_redirect_map in sample/bpf and send pkts via pktgen cmd:
> ./pktgen_sample03_burst_single_flow.sh -i eno1 -d $dst_ip -m $dst_mac -t 10 -s 64
> 
> There are about +/- 0.1M deviation for native testing, the performance
> improved for the base-case, but some drop back with xdp devmap prog attached.
> 
> Version          | Test                           | Generic | Native | Native + 2nd xdp_prog
> 5.10 rc6         | xdp_redirect_map   i40e->i40e  |    2.0M |   9.1M |  8.0M
> 5.10 rc6         | xdp_redirect_map   i40e->veth  |    1.7M |  11.0M |  9.7M
> 5.10 rc6 + patch | xdp_redirect_map   i40e->i40e  |    2.0M |   9.5M |  7.5M
> 5.10 rc6 + patch | xdp_redirect_map   i40e->veth  |    1.7M |  11.6M |  9.1M

I want to highlight the improvement 9.1M -> 9.5M.  This is the native
(40e->i40e) case where the isn't any "2nd xdp_prog".

This means that when we introduced the "2nd xdp_prog", we lost a little
performance without noticing (death-by-a-1000-paper-cuts), for the
baseline case where this feature is not used/activated.

This patch regains that performance for our baseline.  That in itself
make this patch worth it.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer