Conversely, if the load is greater than 1, that means on average, there were processes ready to run, but could not due to CPUs being unavailable. > sysctl -n hw.ncpu 8 > uptime 18:09 up 19 days, 9:06, 3 users, load averages: 2.49 2.04 1.98įor a single-CPU system, if the load is less than 1, that means on average, every process that needed the CPU could use it immediately without being blocked. That is an instantaneous quantity, so utilities such as uptime instead display the exponentially weighted moving average for the past one, five and fifteen minutes rather than the instantaneous number. Load is simply a count of the number of processes using or waiting for the CPU at a single point in time. That’s because there were more processes ready to run than there were CPUs available. In run 2, the OS_CPU_WAIT_TIME of 5,071,200 vs the BUSY_TIME of 1,305,666 means that the system spent almost 4 times the time waiting for the CPU to become available rather than actually running on it. In fact, it’s been said that CPU time is not something that you can save up in the bank to use later.īack to our load test. In business terms, that means you are wasting precious money. In a way, if a system is running at 20% CPU, that just means you are wasting 80% CPU. Hence run 1’s response time is the same as the baseline number even though the CPU usage was as high as 80%. It is also known that under completely no load, a single transaction takes 200 ms. Run 1 had a response time of 200 ms whereas run 2 had a response time of 1500 ms (!). Run 1 - BUSY_TIME 1,159,299 # CPU times are in hundredths of a second IDLE_TIME 286,806 OS_CPU_WAIT_TIME 1,621,100 %busy 80.17 response time 0.2 # seconds Run 2 - BUSY_TIME 1,305,666 IDLE_TIME 125,475 OS_CPU_WAIT_TIME 5,071,200 %busy 91.23 response time 1.5Īlthough CPU usage was quite high in both cases, their performance could not have been more different. The listing below shows the statistics measured during the two runs. Consider two load-test runs, where the exact same system was exposed to two different loads.
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