In-depth analysis of the load of CentOS system

The meaning of load average in the uptime command echo is similar to that of the w command. They both represent the average number of processes in the process queue in the past 1 minute, 5 minutes, and 15 minutes.

What needs to be noted here is the output value of load average. The size of these three values ​​​​can generally not be greater than the number of logical CPUs in the system. For example, in this output, the system has 4 logical CPUs. If the three values ​​​​of load average are long-term When it is greater than 4, it means that the CPU is very busy and the load is very high, which may affect system performance. But occasionally when it is greater than 4, don't worry, it generally will not affect system performance. On the contrary, if the output value of load average is less than the number of CPUs, it means that the CPU is still idle. For example, the output in this example shows that the CPU is relatively idle.

When the CPU is completely idle, the average load is 0; when the CPU workload is saturated, the average load is 1

The system load is 0, which means there is not a single car on the bridge;

The system load is 0.5, which means there are cars on half of the bridge;

The system load is 1.0, which means that there are cars on all sections of the bridge, which means that the bridge is "full". However, it must be noted that the bridge can still pass smoothly until this time;

The system load is 1.7, which means there are too many vehicles, the bridge is already occupied (100%), and the vehicles waiting to get on the bridge behind are 70% of the vehicles on the bridge deck. By analogy, a system load of 2.0 means that there are as many vehicles waiting to get on the bridge as there are vehicles on the bridge deck; a system load of 3.0 means that there are twice as many vehicles waiting to get on the bridge as there are vehicles on the bridge deck. In short, when the system load is greater than 1, the following vehicles must wait; the greater the system load, the longer they must wait to cross the bridge.

The system load of the CPU is basically equivalent to the above analogy. The traffic capacity of the bridge is the maximum workload of the CPU; the vehicles on the bridge are processes waiting for processing by the CPU.

If the CPU processes up to 100 processes per minute, then the system load 0.2 means that the CPU only processes 20 processes in this 1 minute; the system load 1.0 means that the CPU processes exactly 100 processes in this 1 minute; The system load is 1.7, which means that in addition to the 100 processes being processed by the CPU, there are 70 processes queued up waiting for the CPU to process.

When the system load continues to be greater than 0.7, you must start investigating where the problem lies to prevent the situation from getting worse.

When the system load continues to be greater than 1.0, you must find a solution to lower this value.

When the system load reaches 5.0, it means that your system has a serious problem, has not responded for a long time, or is close to crashing. You should not let the system reach this value.

So, 2 CPUs indicate that the system load can reach 2.0, at which time each CPU reaches 100% workload. Broadly speaking, for a computer with n CPUs, the maximum acceptable system load is n.0.

cat /proc/cpuinfo" command can view CPU information. "grep -c 'model name' /proc/cpuinfo" command directly returns the total number of cores of the CPU.

If the system load in only 1 minute is greater than 1.0 and the other two time periods are less than 1.0, this indicates that it is only a temporary phenomenon and the problem is not serious.

If the average system load is greater than 1.0 within 15 minutes (after adjusting the number of CPU cores), it indicates that the problem persists and is not a temporary phenomenon. Therefore, you should mainly observe the "15-minute system load" as an indicator of normal computer operation.

The above is the detailed content of In-depth analysis of the load of CentOS system. For more information, please follow other related articles on the PHP Chinese website!