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Mar
2
awarded  Popular Question
Feb
17
accepted High CPU utilization but low load average
Feb
17
answered High CPU utilization but low load average
Feb
14
comment High CPU utilization but low load average
All information I have found says that threads count as separate processes when seen from the kernel and when calculating load. Hence I fail to see how I could have a multi threaded process on full tilt resulting in 1 load and 100% CPU on a multi-CPU system. Could you please help me understand how you mean?
Feb
13
awarded  Popular Question
Feb
13
comment High CPU utilization but low load average
I just did a test on my own, the threads in a Java process contributes to the load average as if they where separate processes (I.e. a java class that runs 10 threads in a busy-wait loop gives me a load close to 10). I would appreciate a clarification about the threaded process you mentioned above. Thank you!
Feb
13
comment High CPU utilization but low load average
How do you mean that I can have a load of 1 and 100% CPU with a single threaded process? What kind of threads are you talking about? If we consider our Java processes, they have tons of threads, but I was under the assumption that the threads were treated as processes from the perspective of the OS (they have separate PIDs on Linux after all). Could it be so that a single multi threaded java process is only counted as one task from a load average perspective?
Feb
13
awarded  Nice Question
Feb
12
awarded  Commentator
Feb
12
awarded  Editor
Feb
12
revised High CPU utilization but low load average
Clarified that we do not see the stacked CPU utilization in the chart
Feb
12
comment High CPU utilization but low load average
Could you please elaborate yoru last section a bit? I fail to grasp what you mean, while the part of my question you cited is the part I have most trouble understanding.
Feb
12
comment High CPU utilization but low load average
I'm 100% positive that the CPU util we see in the chart is the "average per CPU". Mpstat is run without ALL, but that only leaves out the per-CPU info, the all row still shows the average per CPU. I will clarify the question.
Feb
12
comment High CPU utilization but low load average
It is my understanding that load average also includes the tasks currently executing. That would mean we definitely can have an increase in load average without actual contention for the CPUs. Or am I mistaken/misunderstanding you?
Feb
12
comment High CPU utilization but low load average
Thank you for the suggestion. The chart in my question shows %user time (CPU system time is excluded, we do only see a very slight increase in system time). Could many small tasks be the explanation anyways? If the load average is sampled every 5 seconds, is the CPU utilization data as given by mpstat more frequently sampled?
Feb
12
comment High CPU utilization but low load average
Ah, sorry for misunderstanding you. It would have been a nice explanation, but unfortunately it is the system-wide load average that is shown. I just triple checked.
Feb
12
comment High CPU utilization but low load average
The cpu usage is taken from mpstat, the all row. I am fairly certain it is an average across all CPUs, it is not stacked. For example, when the problem occurs, top shows 2000% CPU usage for one process. That is stacked usage.
Feb
12
comment High CPU utilization but low load average
Do you mean dividing each data point with the number of CPUs? I.e. loadavg/24 in our case? I can easily create such a chart from the data if that helps.
Feb
12
asked High CPU utilization but low load average
Jun
27
accepted Kernel oops on Linux running in VirtualBox breaks some IO-related functionality on the server