[[PageOutline]]

= Performance Tuning =

== System Performance Tuning : Memory ==

 * Share Memory - 有些程式需要用到比較多 Share Memory (共享記憶體), 如: Kerrighed ([wiki:krg_tuning 2008-03-20 (rock/rider)])
{{{
echo "kernel.shmall = 796917578" >> /etc/sysctl.conf
echo "kernel.shmmax = 796917578" >> /etc/sysctl.conf
echo "kernel.shmmni = 4096"      >> /etc/sysctl.conf
}}}

== System Performance Tuning : File System ==

 * /etc/security/limits.conf - 每個程序(process)可以開啟檔案的個數(number limits of open files per process) - 像 HDFS 的 !DataNode 就需要調整這種參數([wiki:jazz/10-02-22#Hadoop:HDFS 2010-02-22])
{{{
#!diff
--- /etc/security/limits.conf 2010-02-22 11:29:11.000000000 +0800
+++ /etc/security/limits.conf.new 2010-02-22 11:28:33.000000000 +0800
@@ -49,4 +49,6 @@
 #ftp             -       chroot          /ftp
 #@student        -       maxlogins       4
 
+*      soft        nofile        8192
+
 # End of file
}}}

== I/O Performance Tuning : NFS ==

 * NFS Tuning - /etc/fstab - 加大 NFS read/write size 可以提升檔案系統的 I/O 效率 ([wiki:krg_tuning 2008-03-20 (rock/rider)])
{{{
192.168.0.111:/home /home nfs rw,bg,soft,intr,rsize=262144,wsize=262144 0 4
192.168.0.111:/opt  /opt  nfs ro,bg,soft,intr,rsize=262144,wsize=262144 0 4
192.168.0.111:/usr  /usr  nfs ro,bg,soft,intr,rsize=262144,wsize=262144 0 4
}}}

== I/O Performance Tuning : IOWait ==

 * [wiki:jazz/10-03-31 2010-03-31] : 高 IOWait 有什麼好的解決之道呢??

== Network Performance Tuning ==

 * TCP Tuning - ([wiki:krg_tuning 2008-03-20 (LSI)])
{{{
echo 262144               > /proc/sys/net/core/rmem_default
echo 8388608              > /proc/sys/net/core/wmem_max
echo 8388608              > /proc/sys/net/core/rmem_max
echo "4096 87380 4194304" > /proc/sys/net/ipv4/tcp_rmem
echo "4096 65536 4194304" > /proc/sys/net/ipv4/tcp_wmem
}}}

 * TCP TIME_WAIT & Reuse - 適用網站伺服器 ([wiki:jazz/Trac_Updates#a2010-03-26 2010-03-26])
{{{
echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout 
sysctl net.ipv4.tcp_tw_reuse=1
sysctl net.ipv4.tcp_tw_recycle=1
}}}

 * 如果沒辦法 ping 224.0.0.1 的話，代表 Broadcast ICMP 封包被濾掉了，因為預設 Linux kernel 2.6 是 disable 的。解法如下：([wiki:jazz/09-09-07 2009-09-07])
{{{
echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
}}}
{{{
~# echo "net.ipv4.icmp_echo_ignore_broadcasts = 0" >> /etc/sysctl.conf
~# sysctl -p
net.ipv4.ip_forward = 1
net.ipv4.icmp_echo_ignore_broadcasts = 0
}}}

== Power Management ==

 * 啟動 SATA ALPM 電源管理功能 - [http://packages.debian.org/powertop powertop] 提供之建議
{{{
echo min_power > /sys/class/scsi_host/host0/link_power_management_policy
}}}

 * 虛擬機器的 clocksource ([wiki/jazz/Trac_Updates#a2010-02-11 2010-02-11])
{{{
echo acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource
}}}

== Security ==

 * 關於 /proc/sysrq-trigger ([wiki:jazz/09-11-17 2009-11-17])
   * [http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/en-US/Reference_Guide/s2-proc-sysrq-trigger.html Redhat 手冊的說明 - /proc/sysrq-trigger]
   * 其實除了 CTRL+ALT+DEL 外，Linux 還可以透過 [http://en.wikipedia.org/wiki/SysRq System Request (Sys Rq) 按鍵] 來做一些特殊除錯工作。這個 Sys Rq 鍵，通常跟 Print Screen 鍵做在一起。
   * 要啟用這個功能，首先必須確認核心的 CONFIG_MAGIC_SYSRQ 參數是否有 enable。
   * [http://en.wikipedia.org/wiki/Magic_SysRq_key 維基百科除了說明 SYSRQ 可以做哪些事情]外，還介紹了[http://julien.danjou.info/sysrqd/ sysrqd]這個軟體，讓管理者可以遠端執行 SYSRQ 的指令。PS.[http://packages.debian.org/sysrqd sysrqd 也有 debian 套件]!!
 * 關於 /proc/sys/kernel/sysrq ([wiki:jazz/09-11-17 2009-11-17])
   * [http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/en-US/Reference_Guide/s3-proc-sys-kernel.html Redhat 手冊的說明 - /proc/sys/kernel/ 底下的檔案意涵]
   * [http://lxr.linux.no/#linux+v2.6.31/Documentation/sysrq.txt Linux 核心關於 SysRq 的說明]