Factor tune_system() out of multinode-demo/ (#4138)

* Remove x bit from ulimit-n.sh

* Factor tune_system() out of multinode-demo/

scripts/tune-system.sh

@@ -0,0 +1,40 @@
+# |source| this file
+#
+# Adjusts system settings for optimal fullnode performance
+#
+
+# shellcheck source=scripts/ulimit-n.sh
+source "$(dirname "${BASH_SOURCE[0]}")"/ulimit-n.sh
+
+# Reference: https://medium.com/@CameronSparr/increase-os-udp-buffers-to-improve-performance-51d167bb1360
+if [[ $(uname) = Linux ]]; then
+  (
+    set -x +e
+    # test the existence of the sysctls before trying to set them
+    # go ahead and return true and don't exit if these calls fail
+    sysctl net.core.rmem_max 2>/dev/null 1>/dev/null &&
+        sudo sysctl -w net.core.rmem_max=161061273 1>/dev/null 2>/dev/null
+
+    sysctl net.core.rmem_default 2>/dev/null 1>/dev/null &&
+        sudo sysctl -w net.core.rmem_default=161061273 1>/dev/null 2>/dev/null
+
+    sysctl net.core.wmem_max 2>/dev/null 1>/dev/null &&
+        sudo sysctl -w net.core.wmem_max=161061273 1>/dev/null 2>/dev/null
+
+    sysctl net.core.wmem_default 2>/dev/null 1>/dev/null &&
+        sudo sysctl -w net.core.wmem_default=161061273 1>/dev/null 2>/dev/null
+  ) || true
+fi
+
+if [[ $(uname) = Darwin ]]; then
+  (
+    if [[ $(sysctl net.inet.udp.maxdgram | cut -d\  -f2) != 65535 ]]; then
+      echo "Adjusting maxdgram to allow for large UDP packets, see BLOB_SIZE in src/packet.rs:"
+      set -x
+      sudo sysctl net.inet.udp.maxdgram=65535
+    fi
+  )
+
+fi
+
+