| Tunable parameter | Default value | Option description |
|---|---|---|
/proc/sys/net/core/rmem_default | "110592" | Defines the default receive window size; for a large BDP, the size should be larger. |
/proc/sys/net/core/rmem_max | "110592" | Defines the maximum receive window size; for a large BDP, the size should be larger. |
/proc/sys/net/core/wmem_default | "110592" | Defines the default send window size; for a large BDP, the size should be larger. |
/proc/sys/net/core/wmem_max | "110592" | Defines the maximum send window size; for a large BDP, the size should be larger. |
/proc/sys/net/ipv4/tcp_window_scaling | "1" | Enables window scaling as defined by RFC 1323; must be enabled to support windows larger than 64KB. |
/proc/sys/net/ipv4/tcp_sack | "1" | Enables selective acknowledgment, which improves performance by selectively acknowledging packets received out of order (causing the sender to retransmit only the missing segments); should be enabled (for wide area network communication), but it can increase CPU utilization. |
/proc/sys/net/ipv4/tcp_fack | "1" | Enables Forward Acknowledgment, which operates with Selective Acknowledgment (SACK) to reduce congestion; should be enabled. |
/proc/sys/net/ipv4/tcp_timestamps | "1" | Enables calculation of RTT in a more accurate way (see RFC 1323) than the retransmission timeout; should be enabled for performance. |
/proc/sys/net/ipv4/tcp_mem | "24576 32768 49152" | Determines how the TCP stack should behave for memory usage; each count is in memory pages (typically 4KB). The first value is the low threshold for memory usage. The second value is the threshold for a memory pressure mode to begin to apply pressure to buffer usage. The third value is the maximum threshold. At this level, packets can be dropped to reduce memory usage. Increase the count for large BDP (but remember, it's memory pages, not bytes). |
/proc/sys/net/ipv4/tcp_wmem | "4096 16384 131072" | Defines per-socket memory usage for auto-tuning. The first value is the minimum number of bytes allocated for the socket's send buffer. The second value is the default (overridden by wmem_default) to which the buffer can grow under non-heavy system loads. The third value is the maximum send buffer space (overridden by wmem_max). |
/proc/sys/net/ipv4/tcp_rmem | "4096 87380 174760" | Same as tcp_wmem except that it refers to receive buffers for auto-tuning. |
/proc/sys/net/ipv4/tcp_low_latency | "0" | Allows the TCP/IP stack to give deference to low latency over higher throughput; should be disabled. |
/proc/sys/net/ipv4/tcp_westwood | "0" | Enables a sender-side congestion control algorithm that maintains estimates of throughput and tries to optimize the overall utilization of bandwidth; should be enabled for WAN communication. This option is also useful for wireless interfaces, as packet loss may not be caused by congestion. |
/proc/sys/net/ipv4/tcp_bic | "1" | Enables Binary Increase Congestion for fast long-distance networks; permits better utilization of links operating at gigabit speeds; should be enabled for WAN communication. |
References
- http://www.ibm.com/developerworks/library/l-hisock/
- http://www.redhat.com/promo/summit/2008/downloads/pdf/Thursday/Mark_Wagner.pdf
- http://www.ntop.org/products/pf_ring/hardware-packet-filtering
