．https://blogs.dropbox.com/tech/2017/09/optimizing-web-servers-for-high-throughput-and-low-latency/

http://www.queryadmin.com/1654/tuning-linux-kernel-tcp-parameters-sysctl/

https://blogs.dropbox.com/tech/2017/09/optimizing-web-servers-for-high-throughput-and-low-latency/
Don’t USE

net.ipv4.tcp_tw_recycle=1
—don’t use it—it was already broken for users behind NAT, but if you upgrade your kernel, it will be broken for everyone.

net.ipv4.tcp_timestamps=0
—don’t disable them unless you know all side-effects and you are OK with them. For example, one of non-obvious side effects is that you will loose window scaling and SACK options on syncookies.

https://read01.com/zh-tw/KBgmj7.html
Don’t USE

net.ipv4.tcp_tw_recycle=1
net.ipv4.tcp_tw_reuse=1  /*Only you know, sometime can do*/

***********sysctl**************
net.ipv4.tcp_mtu_probing=1

# Increase number of max open-files
fs.file-max = 150000

# Increase max number of PIDs
kernel.pid_max = 4194303

# Increase range of ports that can be used
net.ipv4.ip_local_port_range = 1024 65535

# https://tweaked.io/guide/kernel/
# Forking servers, like PostgreSQL or Apache, scale to much higher levels of concurrent connections if this is made larger
kernel.sched_migration_cost_ns=5000000

# https://tweaked.io/guide/kernel/
# Various PostgreSQL users have reported (on the postgresql performance mailing list) gains up to 30% on highly concurrent workloads on multi-core systems
kernel.sched_autogroup_enabled = 0

# https://github.com/ton31337/tools/wiki/tcp_slow_start_after_idle—tcp_no_metrics_save-performance
# Avoid falling back to slow start after a connection goes idle
net.ipv4.tcp_slow_start_after_idle=0
net.ipv4.tcp_no_metrics_save=0

# https://github.com/ton31337/tools/wiki/Is-net.ipv4.tcp_abort_on_overflow-good-or-not%3F
net.ipv4.tcp_abort_on_overflow=0

# Enable TCP window scaling (enabled by default)
# https://en.wikipedia.org/wiki/TCP_window_scale_option
net.ipv4.tcp_window_scaling=1

# Enables fast recycling of TIME_WAIT sockets.
# (Use with caution according to the kernel documentation!)
#net.ipv4.tcp_tw_recycle = 1

# Allow reuse of sockets in TIME_WAIT state for new connections
# only when it is safe from the network stack’s perspective.
#net.ipv4.tcp_tw_reuse = 1

# Turn on SYN-flood protections
net.ipv4.tcp_syncookies=1

# Only retry creating TCP connections twice
# Minimize the time it takes for a connection attempt to fail
net.ipv4.tcp_syn_retries=2
net.ipv4.tcp_synack_retries=2
net.ipv4.tcp_orphan_retries=2

# How many retries TCP makes on data segments (default 15)
# Some guides suggest to reduce this value
net.ipv4.tcp_retries2=8

# Optimize connection queues
# https://www.linode.com/docs/web-servers/nginx/configure-nginx-for-optimized-performance
# Increase the number of packets that can be queued
net.core.netdev_max_backlog = 3240000
# Max number of “backlogged sockets” (connection requests that can be queued for any given listening socket)
net.core.somaxconn = 50000
# Increase max number of sockets allowed in TIME_WAIT
net.ipv4.tcp_max_tw_buckets = 1440000
# Number of packets to keep in the backlog before the kernel starts dropping them
# A sane value is net.ipv4.tcp_max_syn_backlog = 3240000
net.ipv4.tcp_max_syn_backlog = 3240000

# TCP memory tuning
# View memory TCP actually uses with: cat /proc/net/sockstat
# *** These values are auto-created based on your server specs ***
# *** Edit these parameters with caution because they will use more RAM ***
# Changes suggested by IBM on https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/Welcome%20to%20High%20Performance%20Computing%20%28HPC%29%20Central/page/Linux%20System%20Tuning%20Recommendations
# Increase the default socket buffer read size (rmem_default) and write size (wmem_default)
# *** Maybe recommended only for high-RAM servers? ***
net.core.rmem_default=16777216
net.core.wmem_default=16777216
# Increase the max socket buffer size (optmem_max), max socket buffer read size (rmem_max), max socket buffer write size (wmem_max)
# 16MB per socket - which sounds like a lot, but will virtually never consume that much
# rmem_max over-rides tcp_rmem param, wmem_max over-rides tcp_wmem param and optmem_max over-rides tcp_mem param
net.core.optmem_max=16777216
net.core.rmem_max=16777216
net.core.wmem_max=16777216
# Configure the Min, Pressure, Max values (units are in page size)
# Useful mostly for very high-traffic websites that have a lot of RAM
# Consider that we already set the *_max values to 16777216
# So you may eventually comment these three lines
net.ipv4.tcp_mem=16777216 16777216 16777216
net.ipv4.tcp_wmem=4096 87380 16777216
net.ipv4.tcp_rmem=4096 87380 16777216

# Keepalive optimizations
# By default, the keepalive routines wait for two hours (7200 secs) before sending the first keepalive probe,
# and then resend it every 75 seconds. If no ACK response is received for 9 consecutive times, the connection is marked as broken.
# The default values are: tcp_keepalive_time = 7200, tcp_keepalive_intvl = 75, tcp_keepalive_probes = 9
# We would decrease the default values for tcp_keepalive_* params as follow:
net.ipv4.tcp_keepalive_time = 600
net.ipv4.tcp_keepalive_intvl = 10
net.ipv4.tcp_keepalive_probes = 9

# The TCP FIN timeout belays the amount of time a port must be inactive before it can reused for another connection.
# The default is often 60 seconds, but can normally be safely reduced to 30 or even 15 seconds
# https://www.linode.com/docs/web-servers/nginx/configure-nginx-for-optimized-performance
net.ipv4.tcp_fin_timeout = 7

***********sysctl**************

==PS==
．net.ipv4.tcp_slow_start_after_idle & net.ipv4.tcp_no_metrics_save
https://github.com/ton31337/tools/wiki/tcp_slow_start_after_idle—tcp_no_metrics_save-performance