netdev - Re: [PATCH bpf-next] xsk, net: make sock_def

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Message-ID: <38c0f2f6-436d-f0d6-42c6-242e550c06f2@iogearbox.net>
Date:   Wed, 22 Jan 2020 00:36:11 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Björn Töpel <bjorn.topel@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Subject: Re: [PATCH bpf-next] xsk, net: make sock_def_readable() have external
 linkage

On 1/21/20 1:06 PM, Björn Töpel wrote:
> On Tue, 21 Jan 2020 at 01:48, John Fastabend <john.fastabend@...il.com> wrote:
>> Björn Töpel wrote:
>>> From: Björn Töpel <bjorn.topel@...el.com>
>>>
>>> XDP sockets use the default implementation of struct sock's
>>> sk_data_ready callback, which is sock_def_readable(). This function is
>>> called in the XDP socket fast-path, and involves a retpoline. By
>>> letting sock_def_readable() have external linkage, and being called
>>> directly, the retpoline can be avoided.
>>>
>>> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
>>> ---
>>>   include/net/sock.h | 2 ++
>>>   net/core/sock.c    | 2 +-
>>>   net/xdp/xsk.c      | 2 +-
>>>   3 files changed, 4 insertions(+), 2 deletions(-)
>>>
>>
>> I think this is fine but curious were you able to measure the
>> difference with before/after pps or something?
> 
> Ugh, yeah, of course I've should have added that. Sorry for that! Here
> goes; Benchmark is xdpsock rxdrop, NAPI running on core 20:
> 
> **Pre-patch: xdpsock rxdrop: 22.8 Mpps
>   Performance counter stats for 'CPU(s) 20':
> 
>           10,000.58 msec cpu-clock                 #    1.000 CPUs
> utilized
>                  12      context-switches          #    0.001 K/sec
>                   1      cpu-migrations            #    0.000 K/sec
>                   0      page-faults               #    0.000 K/sec
>      29,931,407,416      cycles                    #    2.993 GHz
>      82,538,852,331      instructions              #    2.76  insn per
> cycle
>      15,894,169,979      branches                  # 1589.324 M/sec
>          30,916,486      branch-misses             #    0.19% of all
> branches
> 
>        10.000636027 seconds time elapsed
> 
> **Post-patch: xdpsock rxdrop: 23.2 Mpps
>           10,000.90 msec cpu-clock                 #    1.000 CPUs
> utilized
>                  12      context-switches          #    0.001 K/sec
>                   1      cpu-migrations            #    0.000 K/sec
>                   0      page-faults               #    0.000 K/sec
>      29,932,353,067      cycles                    #    2.993 GHz
>      84,299,636,827      instructions              #    2.82  insn per
> cycle
>      16,228,795,437      branches                  # 1622.733 M/sec
>          28,113,847      branch-misses             #    0.17% of all
> branches
> 
>        10.000596454 seconds time elapsed
> 
> This could fall into the category of noise. :-) PPS and IPC is up a
> bit. OTOH, maybe UDP can benefit from this as well?

Yeah, might be within noise range though getting rid of retpolines in XDP
[socket] fast-path is fine and patch is tiny, so applied, thanks!