Help with load average?


 
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# 1  
Old 09-24-2011
Help with load average?

how load average is calculated and what exactly is it

difference between cpu% and load average
# 2  
Old 09-26-2011
I hope this is not homework.

Load averages are just that - load data gathered over a period of time, then averaged
ex.: disk busy % from iostat command, gathered once an hour
Code:
64%
35%
10%
average=$(( 64 + 35 + 10 ))
average=$((  $average / 3 ))
echo "hourly average = $average"

"load" can be defined as cpu utilization or disk utilization or memory utilization. Or all three. The primary concern about when load becomes an issue is when proccesses are forced to wait for the cpu, wait execessivly for I/O, wait for processes to swap in/out of memory.
# 3  
Old 09-26-2011
Technically, it is the number of blocking processes in the run queue averaged over a certain time period.

Using uptime as an example, the first number is the average over the last minute, the second number is the average over the last five minutes, and the third number is the average over the last 15 minutes.
# 4  
Old 09-26-2011
Quote:
Originally Posted by jim mcnamara
I hope this is not homework.

Load averages are just that - load data gathered over a period of time, then averaged
ex.: disk busy % from iostat command, gathered once an hour
Code:
64%
35%
10%
average=$(( 64 + 35 + 10 ))
average=$((  $average / 3 ))
echo "hourly average = $average"

"load" can be defined as cpu utilization or disk utilization or memory utilization. Or all three. The primary concern about when load becomes an issue is when proccesses are forced to wait for the cpu, wait execessivly for I/O, wait for processes to swap in/out of memory.
thankyou jim
so how to judge what value of load average is good for a system considering approximate value for system resources
# 5  
Old 09-26-2011
Depends what you want it to be. If your system is always busy, high is normal. Low is normal on a mostly idle system.

It's more useful for comparison. Sudden, unexpected changes can be indicative of problems. Low average on a system supposed to be busy -- did some daemon crash and die? High average on usually-idle system -- what's causing it?
# 6  
Old 09-26-2011
Quote:
Originally Posted by Corona688
Depends what you want it to be. If your system is always busy, high is normal. Low is normal on a mostly idle system.

It's more useful for comparison. Sudden, unexpected changes can be indicative of problems. Low average on a system supposed to be busy -- did some daemon crash and die? High average on usually-idle system -- what's causing it?
just for analysis, is there any theroy to calculate threshold value for any given machine
# 7  
Old 09-26-2011
threshold of what?

The raw value only tells you how busy it is, not how busy it should be. It's more useful for comparison. Sudden, unexpected changes can be indicative of problems.

Once it gets above 1 I'd call the machine very busy, and above 2 I'd call overloaded, but ymmv. You can tune a machine to work well even under high loads.

Last edited by Corona688; 09-26-2011 at 03:03 PM..
 
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