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From:   Vasiliy Khoruzhick <vasilykh@arista.com>
Date:   Tue, 11 Sep 2018 11:23:18 -0700
Message-ID: <CAL0zPMPx3B+TXvHTzAW+RcgO6a6jPN47zS8E6nA4+2cRzFM+Tg@mail.gmail.com>
Subject: Re: [PATCH v2] neighbour: confirm neigh entries when ARP packet is received
To:     Stephen Hemminger <stephen@networkplumber.org>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Roopa Prabhu <roopa@cumulusnetworks.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        Jim Westfall <jwestfall@surrealistic.net>,
        Wolfgang Bumiller <w.bumiller@proxmox.com>,
        Vasily Khoruzhick <anarsoul@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Ihar Hrachyshka <ihrachys@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Tue, Sep 11, 2018 at 11:12 AM, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Tue, 11 Sep 2018 11:04:06 -0700
> Vasily Khoruzhick <vasilykh@arista.com> wrote:
>
>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
>> index aa19d86937af..56a554597db5 100644
>> --- a/net/core/neighbour.c
>> +++ b/net/core/neighbour.c
>> @@ -1180,6 +1180,12 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
>>               lladdr = neigh->ha;
>>       }
>>
>> +     /* Update confirmed timestamp for neighbour entry after we
>> +      * received ARP packet even if it doesn't change IP to MAC binding.
>> +      */
>> +     if (new & NUD_CONNECTED)
>> +             neigh->confirmed = jiffies;
>
> You might want to do:
>         if ((new & NUD_CONNECTED) && neigh->confirmed != jiffies)
>                 neigh->confirmed = jiffies;
>
> This avoid poisoning the cacheline with unnecessary write.

Sorry for duplicate - this time in plain text, so it should get
through lkml filter:

I don't think that it's performance-critical path, so this
optimization is unnecessary
and it doesn't improve code readability.