Custom Sysctl settings

sysctl_custom.conf

# WARNING: know why you are changing every single sysctl option.  Do not blindly change them.
# You need to understand the effects of each setting.  For some settings, you may want to 
# increment until errors subside, rather than increasing the values to their max values.
# References:
#   https://access.redhat.com/sites/default/files/attachments/20150325_network_performance_tuning.pdf
#   https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
#   Red Hat Tuned profiles

# Adapter Queue
# Maximum number of packets taken from all interfaces in one polling cycle
# (NAPI poll). In one polling cycle interfaces which are registered to polling
# are probed in a round-robin manner.
# Default: 300
#   check for increments in third column of /proc/net/softnet_stat
net.core.netdev_budget = 10000

# Adapter Queue
# The netdev_max_backlog is a queue within the Linux kernel where traffic is
# stored after reception from the NIC, but before processing by the protocol
# stacks (IP, TCP, etc.). There is one backlog queue per CPU core.  A given
# core's queue can grow automatically, containing a number of packets up to the
# maximum specified by the netdev_max_backlog setting. The netif_receive_skb()
# kernel function will find the corresponding CPU for a packet, and enqueue
# packets in that CPU's queue.  If the queue for that processor is full and
# already at maximum size, packets will be dropped.
# Default: 1000
#   check for increments in second column of /proc/net/softnet_stat
net.core.netdev_max_backlog = 100000

# TCP Listen Backlog
# When a TCP socket is opened by a server in LISTEN state, that socket has a
# maximum number of unaccepted client connections it can handle.  If an
# application is slow at processing client connections, or the server gets may
# new connections rapidly (commonly known as SYN flood), the new connections
# may be lost of specially crafted reply packets known as "SYN cookies" may be
# sent. Tune the system to avoid them. 
# Default: 128
#   check /var/log/messages for SYN cookies
#   check for increments in `netstat -s | grep "listen queue of a socket overflowed"`
net.core.somaxconn = 2048

# TCP Buffer Tuning
# Once network traffic is process from the network adapter, reception directly
# into the application is attempted.  If that is not possible, data is queued
# on the applications socket buffer.  If the receive queue is full, the TCP
# stack will call a routing which "collapses" the receive queue.  If collapsing
# fails to free sufficient space for additional traffic, then data is "pruned",
# i.e. data is dropped from memory and the packet is lost.  Tune around this
# condition to avoide the buffer collapsing and pruning altogether.
# Default: 4096	87380 2916352
#   check for increments in `netstat -s | egrep '(prune|collapse)'`
net.ipv4.tcp_rmem = 4096 87380 16777216

# UDP Buffer Tuning
# The only available tuning for UDP comprises of increasing the receive buffer
# size.  If netstat -us reports UDP "packet receive errors", tune the buffer.
# Default: 124928
#   check for increments in `netstat -s | grep "packet receive errors"` under UDP stats
net.core.rmem_max = 16777216

# Maximizing I/O Throughput
# Minimal preemption granularity for CPU-bound tasks:
# (default: 1 msec#  (1 + ilog(ncpus)), units: nanoseconds)
kernel.sched_min_granularity_ns = 10000000

# SCHED_OTHER wake-up granularity.
# (default: 1 msec#  (1 + ilog(ncpus)), units: nanoseconds)
#
# This option delays the preemption effects of decoupled workloads
# and reduces their over-scheduling. Synchronous workloads will still
# have immediate wakeup/sleep latencies.
kernel.sched_wakeup_granularity_ns = 15000000

# If a workload mostly uses anonymous memory and it hits this limit, the entire
# working set is buffered for I/O, and any more write buffering would require
# swapping, so it's time to throttle writes until I/O can catch up.  Workloads
# that mostly use file mappings may be able to use even higher values.
#
# The generator of dirty data starts writeback at this percentage (system default
# is 20%)
vm.dirty_ratio = 40

# Filesystem I/O is usually much more efficient than swapping, so try to keep
# swapping low.  It's usually safe to go even lower than this on systems with
# server-grade storage.
vm.swappiness = 10