netdev - Re: [PATCH] net-tcp: extend tcp_tw_reuse sysctl to enable loopback only optimization

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Date:   Mon, 04 Jun 2018 17:13:22 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     zenczykowski@...il.com
Cc:     maze@...gle.com, edumazet@...gle.com, netdev@...r.kernel.org,
        ncardwell@...gle.com, ycheng@...gle.com, weiwan@...gle.com
Subject: Re: [PATCH] net-tcp: extend tcp_tw_reuse sysctl to enable loopback
 only optimization

From: "Maciej Żenczykowski" <zenczykowski@...il.com>
Date: Sun,  3 Jun 2018 10:41:17 -0700

> From: Maciej Żenczykowski <maze@...gle.com>
> 
> This changes the /proc/sys/net/ipv4/tcp_tw_reuse from a boolean
> to an integer.
> 
> It now takes the values 0, 1 and 2, where 0 and 1 behave as before,
> while 2 enables timewait socket reuse only for sockets that we can
> prove are loopback connections:
>   ie. bound to 'lo' interface or where one of source or destination
>   IPs is 127.0.0.0/8, ::ffff:127.0.0.0/104 or ::1.
> 
> This enables quicker reuse of ephemeral ports for loopback connections
> - where tcp_tw_reuse is 100% safe from a protocol perspective
> (this assumes no artificially induced packet loss on 'lo').
> 
> This also makes estblishing many loopback connections *much* faster
> (allocating ports out of the first half of the ephemeral port range
> is significantly faster, then allocating from the second half)
> 
> Without this change in a 32K ephemeral port space my sample program
> (it just establishes and closes [::1]:ephemeral -> [::1]:server_port
> connections in a tight loop) fails after 32765 connections in 24 seconds.
> With it enabled 50000 connections only take 4.7 seconds.
> 
> This is particularly problematic for IPv6 where we only have one local
> address and cannot play tricks with varying source IP from 127.0.0.0/8
> pool.
> 
> Signed-off-by: Maciej Żenczykowski <maze@...gle.com>

Applied, thank you.