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0. 概要
本文将介绍一个用于监控一组进程CPU使用率的Shell脚本，，当检测到某进程的CPU使用率超出阈值时，使用 perf 工具抓取该进程的详细信息。
本shell脚本为了能在普通嵌入式系统上运行做了妥协和优化。
1. shell脚本流程的简要图示：
2. perf介绍
perf 是 Linux 内核提供的一个强大性能分析工具，能够用于分析和调优系统性能。它支持多种事件类型，如CPU时钟、缓存命中/未命中、中断等。
在本脚本中，当某个进程的CPU使用率超过设定阈值（例如80%）时，会使用以下命令抓取该进程的详细性能数据：
perf record -F 99 -e cpu-clock -p $pid -g -o "perf-$process_name.data" -- sleep $perf_sleep_time
-F 99：以每秒99次的频率进行采样。-e cpu-clock：采样的事件类型为CPU时钟周期。-p $pid：指定要采样的进程ID。-g：记录调用栈信息，帮助分析性能瓶颈。-o "perf-$process_name.data"：将采样数据输出到指定文件中。-- sleep $perf_sleep_time：持续采样时间为10秒。
通过抓取高CPU使用率进程的详细性能数据，我们可以深入分析性能瓶颈，找出导致高CPU使用的原因，从而进行针对性的优化。
更多介绍请查看:
使用perf(火焰图)查看热点函数和系统调用最大延迟函数
如何使用perf 统计cpu和内存？
3. shell脚本详解
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日志文件配置：
# Log file location LOGFILE="process_monitor.log" # Redirect standard input, output, and error to log file exec 1>>"$LOGFILE" exec 2>>"$LOGFILE"这部分代码配置日志文件，并将标准输入、输出和错误重定向到日志文件中。
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后台运行检测：
# Check if the script is already running if [ "$1" != "background" ]; then"$0" background &exit 0 fi这段代码用于检测脚本是否已经在后台运行，如果没有，则重新以后台模式启动自己。
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初始化上次报告时间文件：
# Initialize last report time file last_report_time_file="last_report_time" touch "$last_report_time_file"初始化用于存储上次报告时间的文件。
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获取CPU总时间的函数：
# Function to get the total CPU usage from /proc/stat get_total_cpu_time() {awk '/^cpu / {print $2 + $3 + $4 + $5 + $6 + $7 + $8}' /proc/stat }从
/proc/stat文件中获取CPU总时间。 -
获取进程CPU时间的函数：
# Function to get the process CPU usage from /proc/[pid]/stat get_process_cpu_time() {pid=$1awk '{print $14 + $15 + $16 + $17}' /proc/$pid/stat }从
/proc/[pid]/stat文件中获取指定进程的CPU时间。 -
计算进程CPU使用率的函数：
# Function to calculate CPU usage of a process calculate_cpu_usage() {pid=$1prev_process_time=$(get_process_cpu_time "$pid")prev_total_time=$(get_total_cpu_time)sleep 1process_time=$(get_process_cpu_time "$pid")total_time=$(get_total_cpu_time)process_delta=$((process_time - prev_process_time))total_delta=$((total_time - prev_total_time))cpu_usage=$((100 * process_delta / total_delta))echo $cpu_usage }计算指定进程的CPU使用率。
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加载上次报告时间的函数：
# Function to load the last report time for a PID load_last_report_time() {pid=$1grep "^$pid=" "$last_report_time_file" | cut -d'=' -f2 }从文件中加载上次报告时间。
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保存上次报告时间的函数：
# Function to save the last report time for a PID save_last_report_time() {pid=$1time=$2sed -i "/^$pid=/d" "$last_report_time_file"echo "$pid=$time" >> "$last_report_time_file" }将上次报告时间保存到文件中。
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进程监控列表：
# List of process names to monitor process_names="top systemd"定义需要监控的进程名称列表。
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监控循环：
while true; docurrent_time=$(date +%s)for process_name in $process_names; doif [ -n "$DEBUG_ON" ]; thenecho "Checking process: $process_name"fi# Find all matching process PIDspids=$(ps aux | grep "$process_name" | grep -v grep | awk '{print $2}')for pid in $pids; do# Calculate CPU usagecpu_usage=$(calculate_cpu_usage "$pid")# Check if CPU usage exceeds $max_cpu_usage%if [ "$cpu_usage" -gt $max_cpu_usage ]; thenecho "High CPU usage detected for process '$process_name' (PID: $pid): $cpu_usage%"# Load the last report time for this PIDlast_time=$(load_last_report_time "$pid")last_time=${last_time:-0}time_diff=$((current_time - last_time))# Check if the last report time is more than 60 seconds agoif [ "$time_diff" -ge 60 ]; thenecho "time_diff: $time_diff, perf record -F 99 -e cpu-clock -p $pid -g -o perf-$process_name.data -- sleep $perf_sleep_time"ps -p "$pid" -o pid,ppid,cmd,%mem,%cpu >> "$LOGFILE"perf record -F 99 -e cpu-clock -p $pid -g -o "perf-$process_name.data" -- sleep $perf_sleep_time# Save the last report time for this PIDsave_last_report_time "$pid" "$current_time"# sleep for 1 secondsleep 1fielseif [ -n "$DEBUG_ON" ]; thenecho "CPU usage for process '$process_name' (PID: $pid): $cpu_usage%"fifidonedonedone这是主要的监控循环，定期检查指定进程的CPU使用率，并在超过阈值时使用 perf 抓取详细信息。
4. 完整脚本实现
以下是优化后的Shell脚本，适用于普通嵌入式系统：
#!/bin/sh# This script monitors the CPU usage of a list of processesDEBUG_ON=1
# Log file location
LOGFILE="process_monitor.log"# Redirect standard input, output, and error to log file
exec 1>>"$LOGFILE"
exec 2>>"$LOGFILE"# Check if the script is already running
if [ "$1" != "background" ]; then"$0" background &exit 0
fi# Initialize last report time file
last_report_time_file="last_report_time"
touch "$last_report_time_file"# Function to get the total CPU usage from /proc/stat
get_total_cpu_time() {awk '/^cpu / {print $2 + $3 + $4 + $5 + $6 + $7 + $8}' /proc/stat
}# Function to get the process CPU usage from /proc/[pid]/stat
get_process_cpu_time() {pid=$1awk '{print $14 + $15 + $16 + $17}' /proc/$pid/stat
}# Function to calculate CPU usage of a process
calculate_cpu_usage() {pid=$1prev_process_time=$(get_process_cpu_time "$pid")prev_total_time=$(get_total_cpu_time)sleep 1process_time=$(get_process_cpu_time "$pid")total_time=$(get_total_cpu_time)process_delta=$((process_time - prev_process_time))total_delta=$((total_time - prev_total_time))cpu_usage=$((100 * process_delta / total_delta))echo $cpu_usage
}# Function to load the last report time for a PID
load_last_report_time() {pid=$1grep "^$pid=" "$last_report_time_file" | cut -d'=' -f2
}# Function to save the last report time for a PID
save_last_report_time() {pid=$1time=$2sed -i "/^$pid=/d" "$last_report_time_file"echo "$pid=$time" >> "$last_report_time_file"
}# List of process names to monitor
process_names="top systemd"echo "Monitoring CPU usage for processes: $process_names"# Perf sleep time
perf_sleep_time=10
max_cpu_usage=80# Monitoring loop
while true; docurrent_time=$(date +%s)for process_name in $process_names; doif [ -n "$DEBUG_ON" ]; thenecho "Checking process: $process_name"fi# Find all matching process PIDs# pids=$(ps | grep "$process_name" | grep -v grep | awk '{print $1}')pids=$(ps aux | grep "$process_name" | grep -v grep | awk '{print $2}')for pid in $pids; do# Calculate CPU usagecpu_usage=$(calculate_cpu_usage "$pid")# Check if CPU usage exceeds $max_cpu_usage%if [ "$cpu_usage" -gt $max_cpu_usage ]; thenecho "High CPU usage detected for process '$process_name' (PID: $pid): $cpu_usage%"# Load the last report time for this PIDlast_time=$(load_last_report_time "$pid")last_time=${last_time:-0}time_diff=$((current_time - last_time))# Check if the last report time is more than 60 seconds agoif [ "$time_diff" -ge 60 ]; thenecho "time_diff: $time_diff, perf record -F 99 -e cpu-clock -p $pid -g -o perf-$process_name.data -- sleep $perf_sleep_time"ps -p "$pid" -o pid,ppid,cmd,%mem,%cpu >> "$LOGFILE"perf record -F 99 -e cpu-clock -p $pid -g -o "perf-$process_name.data" -- sleep $perf_sleep_time# Save the last report time for this PIDsave_last_report_time "$pid" "$current_time"# sleep for 1 secondsleep 1fielseif [ -n "$DEBUG_ON" ]; thenecho "CPU usage for process '$process_name' (PID: $pid): $cpu_usage%"fifidonedonedone通过这种方式，我们可以有效地监控嵌入式系统中高CPU使用率的进程，并通过 perf 工具获取详细的性能数据，帮助我们进行性能调优和问题排查。