Detailed explanation of the process of troubleshooting the cause of high CPU usage under Linux

Preface

High CPU usage is a common online problem. If you don't know how to do this, it's really a bit disappointing.

Don't worry, brother, I'll teach you a combo.

start

Let's start with a project. The entire API, when we request /cpu/{count}, we can manually increase the CPU. Smart ghost~

    @GetMapping("/cpu/{count}")
    public long cpuTest(@PathVariable("count") long count) {
        long number = 0;
        for (int i = 0; i < count; i++) {
            number++;
        }
        return number;
    }

Pack, upload, and start

It's running. Remember the process number 14849.

Let's first look at the CPU usage under normal circumstances.

Very reasonable

Simulate online CPU surge

We request the /cpu/{100000000000} interface to increase the CPU usage, and use top to observe the CPU usage.

Directly work to 98%, very nice

OK, let's get started. We have a problem online now. The CPU is always very high. The boss asked you to find the reason and start to support it.

In fact, we now know who raised the CPU, but it is not detailed enough. It is far from enough to know which project has the problem. We should find the culprit, which method and how many lines caused the problem, so that the boss can call him an expert.

step

jps+top locates the application process

pidtop -Hp {pid} find the thread tid

Convert tid to hexadecimal printf "%x\n" {tid}

Print stack information jstack

Filter out what we want

Troubleshooting

The process id has been determined to be 14849. The next step is to find which thread is causing the problem.

Top -Hp 14849

It's obviously this 14908 who did it.

Convert to hexadecimal

Print Stack

The stack trace shows that the problem is on line 20 in TestController. Let’s go into code verification.

No big problem

Solve the case

Sprinkle flowers

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