{"id":900,"date":"2026-08-17T22:53:41","date_gmt":"2026-08-17T22:53:41","guid":{"rendered":"https:\/\/bestdedicatedwebhostingserver.com\/blog\/?p=900"},"modified":"2026-10-20T22:06:02","modified_gmt":"2026-10-20T22:06:02","slug":"game-server-udp-buffer-sizing-rmem-max","status":"publish","type":"post","link":"https:\/\/bestdedicatedwebhostingserver.com\/blog\/game-server-udp-buffer-sizing-rmem-max\/","title":{"rendered":"Game Server UDP Buffer Sizing: net.core.rmem_max and the Drops Nobody Logs"},"content":{"rendered":"
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Almost every game server tutorial you have read says “increase the socket buffers” and stops there. In practice, undersized UDP receive buffers are one of the most common causes of a server that reports perfect CPU and RAM utilisation while players still see hit-registration gaps, rubber-banding, or “Connection timed out” during a base raid. The kernel silently drops datagrams that arrive when the socket queue is full, and nothing in the game logs tells you. This is a measurement and platform problem as much as a tuning one, which is why operators who run their own bare-metal game servers with full kernel access<\/a> have a decisive advantage over managed shared plans that hide sysctl<\/code>.<\/p>\n

What Actually Happens When the Buffer Fills<\/h2>\n

Each UDP socket has two limits: net.core.rmem_default<\/code> (what a socket gets without asking) and net.core.rmem_max<\/code> (the ceiling a program can request with SO_RCVBUF<\/code>). Linux doubles the value you set, so an rmem_max<\/code> of 4 MiB yields an 8 MiB effective receive buffer. When the queue is full, the kernel drops the newest packet and increments the RcvbufErrors<\/code> counter in \/proc\/net\/snmp<\/code> under Udp:<\/code>.<\/p>\n

The relevant columns are InErrors, which includes buffer drops, and NoPorts. If InErrors climbs during peak load while the CPU is idle, you have a buffer or scheduling problem, not a game-code problem.<\/p>\n

# watch UDP buffer drops once per second\nwatch -n1 \"awk '\/^Udp:\/{getline v; print v}' \/proc\/net\/snmp\"<\/code><\/pre>\n
How Much Buffer a Game Server Really Needs<\/h2>\n
The buffer must cover the worst burst, not the average rate. A practical estimate:<\/p>\n\n\n\n\n\n\n
Workload<\/th>\nAvg packet rate<\/th>\nPeak burst (5 s)<\/th>\nSuggested rmem_max<\/th>\n<\/tr>\n
Minecraft (64 players)<\/td>\n~6k pkt\/s<\/td>\n12k pkt\/s<\/td>\n4 MiB<\/td>\n<\/tr>\n
CS2 (20 slots, 128 tick)<\/td>\n~9k pkt\/s<\/td>\n22k pkt\/s<\/td>\n8 MiB<\/td>\n<\/tr>\n
Rust (200 players, raid)<\/td>\n~25k pkt\/s<\/td>\n70k pkt\/s<\/td>\n16 MiB<\/td>\n<\/tr>\n
FiveM (128 slots, OneSync)<\/td>\n~30k pkt\/s<\/td>\n90k pkt\/s<\/td>\n32 MiB<\/td>\n<\/tr>\n<\/table>\n
Convert burst to bytes: at ~280 bytes average UDP payload plus ~60 bytes of headers and sk_buff overhead, 70k pkt\/s is roughly 24 MB\/s. A buffer of 16 MiB therefore holds under one second of traffic. That is the design target: enough to ride out a 200\u2013400 ms scheduler stall or NIC interrupt storm without dropping a frame of input.<\/p>\n
Tuning Values That Hold Up Under Load<\/h2>\n