linux-kernel - RE: epoll_wait() performance

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Message-ID: <1265e30d04484d08b86ba2abef5f5822@AcuMS.aculab.com>
Date:   Thu, 28 Nov 2019 10:17:34 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Eric Dumazet' <eric.dumazet@...il.com>,
        'Paolo Abeni' <pabeni@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
CC:     'Marek Majkowski' <marek@...udflare.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        network dev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...udflare.com>
Subject: RE: epoll_wait() performance

From: Eric Dumazet
> Sent: 27 November 2019 17:47
...
> A QUIC server handles hundred of thousands of ' UDP flows' all using only one UDP socket
> per cpu.
> 
> This is really the only way to scale, and does not need kernel changes to efficiently
> organize millions of UDP sockets (huge memory footprint even if we get right how
> we manage them)
> 
> Given that UDP has no state, there is really no point trying to have one UDP
> socket per flow, and having to deal with epoll()/poll() overhead.

How can you do that when all the UDP flows have different destination port numbers?
These are message flows not idempotent requests.
I don't really want to collect the packets before they've been processed by IP.

I could write a driver that uses kernel udp sockets to generate a single message queue
than can be efficiently processed from userspace - but it is a faff compiling it for
the systems kernel version.

	David

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