Linux CPU load average
Hey,
I have a small query regarding the load averages on a multi-core machines. If a single core machine has load avg of 1,does it mean that CPU utilization is 100 %? For a dual core,does a load of 2.0 mean ,the cpu utilization is 100 % or 50 %? my machine specs are: Code:
grep -i siblings /proc/cpuinfo my calculation is Code:
cores loadavg cpu % Thanks ! |
Almost. Linux includes processes in I/O wait, so CPU utilization doesn't map directly to load. A system can have a low CPU utilization and still have a high load in this case. See the Wikipedia description.
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From wikipedia
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-for last minute the cpu was overloaded by 73% i.e 73/2 = 36% per proc ? -for last 5 minute the cpu was under loaded by 50% i.e 50/2 = 25% per proc ? |
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1 core and 1 loadavg means 100% CPU utilization. For 2 cores the loadavg has to be 2 to mean 100% CPU utilization. A loadavg of .75 should signal the System Admin to look into it before the system/server gets worse- a proactive action. A loadavg of .9 and above means critical state and requires immediate action to be taken to prevent a system crash! Well, the system may not crash at all but a lot of jobs can fail to run. I have seen it practially. Once I was working for a client and the server's loadavg reached so much hight that even "clear" would fail to run. |
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The better way to think of load on Linux is as a measure of system response time. The higher the number, the less responsive. If you want a measure of CPU load exclusively, use top or sar. |
Dodgy software can place threads (incorrectly) in uninterrupable sleep, and drive the load way past 100 - with no (response) effect on anything. Apache for example.
loadavg, like %wa, is a barely useful metric. Especially when it's not properly understood, and interpreted in relation to the specific computing environment involved. |
To clarify, the response time I was referring to is process response time (how quickly processes are being serviced), not interactive response. You're correct that interactive response may not be impacted at all, even with a high load.
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