Performance tuning problem --Load averages

[watermelonyu]

top 中的 load average 對 performance 的真正影響為何?



通常聽到的說法是, 如果 CPU 有 4 顆, load average 超過 8 (CPU 個數的兩倍) 的時候, 代表 CPU 的 loading 很重, 但往往此時還有 idle, 也許是 10% ~ 20%, 雖然有 idle 但真的覺得慢

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The load average numbers give the number of jobs in the run queue for the last 5 seconds, the last 30 seconds, and the last 60 seconds. The Mach factor is a variant of the load average, given for the same intervals; the

closer its value to 0, the higher the load.

[watermelonyu]

run queue is the current instantaneous

number of processes waiting to use cpu.



As the words, load average is the 1,5,

and 15 minutes average of cpu load,

it include short sleepers, so, it is

possible to have a high load and idle cpu.



the run queue only includes processes

that are in the SRUN or TSRUN state, that

is they are in the queue for some cpu.

short sleepers will generally run soon

and so should be considered part of the

cpu load.

[watermelonyu]

曾經看過一篇文章:

1. 如果load average/CPU數量 < 3, performance is good

2. 如果load average/CPU數量 > 5, performance is very bad

[watermelonyu]

hp討論區有解釋過了

top and uptime 看到的load average值

拿來系統負載評估並不準確

http://www1.itrc.hp.com/service/cki/docDisplay.do?docLocale=zh_TW&docId=200000074260841

[watermelonyu]

對於 HP-UX 而言, 也許不是很準確(沒有長期 monitor 的經驗), 但對於 Tru64 而言, 卻很有用, 我們長期觀察 load averages, 發現超過 CPU 數兩倍之後, 的確感覺到慢



所以才想聽聽大家實際的管理心得



Thanks