netdev - Re: [net-next PATCH 0/3] net: optimize ICMP-reply code path

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Message-ID: <1483984610.5846.12.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Mon, 09 Jan 2017 09:56:50 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [net-next PATCH 0/3] net: optimize ICMP-reply code path

On Mon, 2017-01-09 at 09:43 -0800, Cong Wang wrote:
> On Mon, Jan 9, 2017 at 7:03 AM, Jesper Dangaard Brouer
> <brouer@...hat.com> wrote:
> >
> > Use-case: The specific case I experienced this being a bottleneck is,
> > sending UDP packets to a port with no listener, which obviously result
> > in kernel replying with ICMP Destination Unreachable (type:3), Port
> > Unreachable (code:3), which cause the bottleneck.
> 
> Why this is a case we should care about for performance?

This is called provisioning.

If you have a server farm that was qualified to handle 100 Mpps,
you want to absorb these 100 Mpps, even if the UDP server is restarted
in a clean or catastrophic mode.

The catastrophic mode would be the case that Jesper described : No UDP
socket is bound and ready to receive packets.