// 示例：Java 應(yīng)用在不同內(nèi)核版本下的線程調(diào)度表現(xiàn)差異
public class KernelPerformanceTest {
    public static void main(String[] args) throws InterruptedException {
        int threadCount = Runtime.getRuntime().availableProcessors() * 2;
        System.out.println("可用處理器核心數(shù)：" + Runtime.getRuntime().availableProcessors());
        System.out.println("啟動(dòng) " + threadCount + " 個(gè)線程進(jìn)行壓力測(cè)試...");

        long startTime = System.nanoTime();

        Thread[] threads = new Thread[threadCount];
        for (int i = 0; i < threadCount; i++) {
            threads[i] = new Thread(() -> {
                // 模擬 CPU 密集型任務(wù)
                double result = 0;
                for (int j = 0; j < 10_000_000; j++) {
                    result += Math.sin(j) * Math.cos(j);
                }
                System.out.println(Thread.currentThread().getName() + " 完成計(jì)算: " + result);
            });
            threads[i].start();
        }

        for (Thread t : threads) {
            t.join();
        }

        long endTime = System.nanoTime();
        double duration = (endTime - startTime) / 1_000_000_000.0;
        System.out.printf("總耗時(shí): %.2f 秒%n", duration);

        // 獲取當(dāng)前內(nèi)核版本（需配合 shell 腳本或 JNI）
        try {
            Process p = Runtime.getRuntime().exec("uname -r");
            java.io.BufferedReader reader = new java.io.BufferedReader(
                new java.io.InputStreamReader(p.getInputStream()));
            String kernelVersion = reader.readLine();
            System.out.println("當(dāng)前內(nèi)核版本: " + kernelVersion);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

# 1. 查看當(dāng)前內(nèi)核版本
uname -r

# 2. 查看已安裝內(nèi)核列表
rpm -qa | grep kernel   # CentOS/RHEL/Fedora
dpkg -l | grep linux-image  # Ubuntu/Debian

# 3. 檢查磁盤(pán)空間（至少預(yù)留 500MB）
df -h /boot

# 4. 備份重要數(shù)據(jù)（尤其是 /boot 和 GRUB 配置）
sudo cp -r /boot /boot.backup.$(date +%Y%m%d)
sudo cp /etc/default/grub /etc/default/grub.backup

# 5. 記錄當(dāng)前系統(tǒng)狀態(tài)
cat /proc/version > /tmp/kernel_upgrade_precheck.txt
lspci >> /tmp/kernel_upgrade_precheck.txt
lsmod >> /tmp/kernel_upgrade_precheck.txt

# 更新軟件源
sudo apt update

# 查看可升級(jí)的內(nèi)核包
apt list --upgradable | grep linux-image

# 升級(jí)所有包（包括內(nèi)核）
sudo apt upgrade

# 或僅升級(jí)內(nèi)核相關(guān)包
sudo apt install linux-image-generic linux-headers-generic

# 清理舊內(nèi)核（謹(jǐn)慎操作！）
sudo apt autoremove --purge

# 啟用 ELRepo 倉(cāng)庫(kù)獲取較新內(nèi)核（可選）
sudo yum install -y https://www.elrepo.org/elrepo-release-8.el8.elrepo.noarch.rpm

# 查看可用內(nèi)核
yum --disablerepo="*" --enablerepo="elrepo-kernel" list available

# 安裝最新主線內(nèi)核
sudo yum --enablerepo=elrepo-kernel install kernel-ml

# 設(shè)置默認(rèn)啟動(dòng)內(nèi)核
sudo grub2-set-default 0
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

# 重啟
sudo reboot

cd /usr/src
sudo wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.6.1.tar.xz
sudo tar -xf linux-6.6.1.tar.xz
cd linux-6.6.1

# 使用當(dāng)前配置作為基礎(chǔ)
sudo cp /boot/config-$(uname -r) .config

# 或使用圖形界面配置（需安裝 libncurses-dev）
sudo make menuconfig

# 或使用默認(rèn)配置
sudo make defconfig

# 編譯內(nèi)核（-j 參數(shù)根據(jù) CPU 核心數(shù)調(diào)整）
sudo make -j$(nproc) all

# 安裝模塊
sudo make modules_install

# 安裝內(nèi)核
sudo make install

# 更新引導(dǎo)配置
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

# 重啟
sudo reboot

# 添加 PPA 并安裝
sudo add-apt-repository ppa:teejee2008/ppa
sudo apt update
sudo apt install ukuu

# 圖形界面或命令行使用
sudo ukuu --list
sudo ukuu --install v6.6.1

# 下載并運(yùn)行腳本（示例）
curl -s https://kernel.ubuntu.com/~kernel-ppa/mainline/installer | bash -s -- -v 6.6.1

uname -r
# 輸出示例：6.6.1-060601-generic

dmesg | head -20
journalctl -b | grep -i "error\|fail\|warn"

systemctl list-units --type=service --state=failed
ss -tuln  # 檢查網(wǎng)絡(luò)端口監(jiān)聽(tīng)
df -h     # 檢查文件系統(tǒng)掛載

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.io.IOException;

public class PostUpgradeValidation {

    public static void main(String[] args) {
        System.out.println("?? 開(kāi)始內(nèi)核升級(jí)后 Java 應(yīng)用驗(yàn)證...");

        // 1. 檢查 JVM 運(yùn)行時(shí)信息
        Runtime runtime = Runtime.getRuntime();
        System.out.println("?? JVM 供應(yīng)商: " + System.getProperty("java.vendor"));
        System.out.println("?? JVM 版本: " + System.getProperty("java.version"));
        System.out.println("?? 最大內(nèi)存: " + (runtime.maxMemory() / 1024 / 1024) + " MB");

        // 2. 檢查系統(tǒng)屬性
        System.out.println("?? 操作系統(tǒng): " + System.getProperty("os.name") + " " + System.getProperty("os.version"));
        System.out.println("???  架構(gòu): " + System.getProperty("os.arch"));

        // 3. 獲取內(nèi)核版本（通過(guò)執(zhí)行 shell 命令）
        try {
            Process process = Runtime.getRuntime().exec("uname -r");
            java.util.Scanner scanner = new java.util.Scanner(process.getInputStream()).useDelimiter("\\A");
            String kernelVersion = scanner.hasNext() ? scanner.next().trim() : "未知";
            System.out.println("?? 當(dāng)前內(nèi)核版本: " + kernelVersion);

            // 4. 檢查是否為預(yù)期版本（示例：期望 >= 6.0）
            if (compareKernelVersion(kernelVersion, "6.0") < 0) {
                System.err.println("? 內(nèi)核版本過(guò)低！期望 >= 6.0，當(dāng)前為 " + kernelVersion);
                System.exit(1);
            } else {
                System.out.println("? 內(nèi)核版本符合要求！");
            }

        } catch (IOException e) {
            System.err.println("?? 無(wú)法獲取內(nèi)核版本: " + e.getMessage());
        }

        // 5. 檢查線程調(diào)度性能（簡(jiǎn)略版）
        testThreadScheduling();

        // 6. 檢查文件 I/O 性能（簡(jiǎn)略版）
        testFileIO();

        System.out.println("?? 所有驗(yàn)證測(cè)試完成！");
    }

    private static int compareKernelVersion(String v1, String v2) {
        String[] parts1 = v1.split("\\.");
        String[] parts2 = v2.split("\\.");
        
        int len = Math.min(parts1.length, parts2.length);
        for (int i = 0; i < len; i++) {
            int num1 = Integer.parseInt(parts1[i].replaceAll("[^0-9]", ""));
            int num2 = Integer.parseInt(parts2[i].replaceAll("[^0-9]", ""));
            if (num1 != num2) return Integer.compare(num1, num2);
        }
        return Integer.compare(parts1.length, parts2.length);
    }

    private static void testThreadScheduling() {
        System.out.println("\n??  測(cè)試線程調(diào)度性能...");

        final int THREAD_COUNT = 4;
        Thread[] threads = new Thread[THREAD_COUNT];
        long startTime = System.nanoTime();

        for (int i = 0; i < THREAD_COUNT; i++) {
            final int id = i;
            threads[i] = new Thread(() -> {
                double sum = 0;
                for (int j = 0; j < 1_000_000; j++) {
                    sum += Math.sqrt(j);
                }
                System.out.println("?? 線程 " + id + " 完成計(jì)算");
            });
            threads[i].start();
        }

        for (Thread t : threads) {
            try { t.join(); } catch (InterruptedException e) { e.printStackTrace(); }
        }

        long duration = System.nanoTime() - startTime;
        System.out.printf("? %d 個(gè)線程調(diào)度完成，耗時(shí) %.2f 毫秒%n", 
            THREAD_COUNT, duration / 1_000_000.0);
    }

    private static void testFileIO() {
        System.out.println("\n?? 測(cè)試文件 I/O 性能...");

        String testFile = "/tmp/kernel_test_io.dat";
        byte[] data = new byte[1024 * 1024]; // 1MB 數(shù)據(jù)

        try {
            // 寫(xiě)入測(cè)試
            long writeStart = System.nanoTime();
            java.io.FileOutputStream fos = new java.io.FileOutputStream(testFile);
            for (int i = 0; i < 10; i++) { // 寫(xiě)入 10MB
                fos.write(data);
            }
            fos.close();
            long writeTime = System.nanoTime() - writeStart;

            // 讀取測(cè)試
            long readStart = System.nanoTime();
            java.io.FileInputStream fis = new java.io.FileInputStream(testFile);
            while (fis.read(data) != -1) {}
            fis.close();
            long readTime = System.nanoTime() - readStart;

            // 清理
            java.nio.file.Files.delete(java.nio.file.Paths.get(testFile));

            System.out.printf("? 文件寫(xiě)入 10MB 耗時(shí): %.2f 毫秒%n", writeTime / 1_000_000.0);
            System.out.printf("? 文件讀取 10MB 耗時(shí): %.2f 毫秒%n", readTime / 1_000_000.0);

        } catch (Exception e) {
            System.err.println("? 文件 I/O 測(cè)試失敗: " + e.getMessage());
        }
    }
}

# Ubuntu
sudo apt remove linux-image-6.6.1-xxx

# CentOS
sudo yum remove kernel-ml-6.6.1

# 重建 GRUB
sudo update-grub   # Ubuntu
sudo grub2-mkconfig -o /boot/grub2/grub.cfg  # CentOS

# 重新安裝驅(qū)動(dòng)（以 Ubuntu 為例）
sudo ubuntu-drivers autoinstall

# 或手動(dòng)指定版本
sudo apt install nvidia-driver-535

# 重啟
sudo reboot

# 重新編譯內(nèi)核模塊
sudo /sbin/vboxconfig   # VirtualBox
sudo vmware-modconfig --console --install-all  # VMware

# /etc/sysctl.conf 末尾添加：

# 增大文件描述符限制（適用于高并發(fā) Netty 應(yīng)用）
fs.file-max = 2097152
fs.nr_open = 2097152

# 優(yōu)化 TCP 棧（適用于 Web 服務(wù)）
net.core.somaxconn = 65535
net.ipv4.tcp_max_syn_backlog = 65535
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 30

# 內(nèi)存管理優(yōu)化
vm.swappiness = 1
vm.dirty_ratio = 15
vm.dirty_background_ratio = 5

# 應(yīng)用更改
sudo sysctl -p

java -server \
     -XX:+UseG1GC \
     -XX:MaxGCPauseMillis=200 \
     -XX:+ParallelRefProcEnabled \
     -XX:+PerfDisableSharedMem \
     -XX:+AlwaysPreTouch \
     -XX:+UnlockExperimentalVMOptions \
     -XX:+UseFastUnorderedTimeStamps \
     -jar your-app.jar

#!/bin/bash
# kernel-upgrade-auto.sh

echo "?? 開(kāi)始自動(dòng)化內(nèi)核升級(jí)流程..."

# 1. 檢查前置條件
if [ $(id -u) -ne 0 ]; then
    echo "? 請(qǐng)以 root 權(quán)限運(yùn)行此腳本"
    exit 1
fi

FREE_SPACE=$(df /boot | tail -1 | awk '{print $4}')
if [ $FREE_SPACE -lt 500000 ]; then
    echo "? /boot 分區(qū)空間不足 500MB，請(qǐng)清理后再試"
    exit 1
fi

# 2. 備份當(dāng)前配置
BACKUP_DIR="/backup/kernel-$(date +%Y%m%d)"
mkdir -p $BACKUP_DIR
cp -r /boot $BACKUP_DIR/boot
cp /etc/default/grub $BACKUP_DIR/grub

echo "? 備份完成"

# 3. 執(zhí)行升級(jí)（以 Ubuntu 為例）
apt update
apt install -y linux-image-generic linux-headers-generic

# 4. 設(shè)置默認(rèn)啟動(dòng)項(xiàng)
update-grub

# 5. 生成驗(yàn)證腳本
cat > /tmp/validate-kernel.java << 'EOF'
public class ValidateKernel {
    public static void main(String[] args) {
        try {
            Process p = Runtime.getRuntime().exec("uname -r");
            java.util.Scanner s = new java.util.Scanner(p.getInputStream());
            String version = s.nextLine();
            System.out.println("? 內(nèi)核升級(jí)成功！當(dāng)前版本: " + version);
            
            // 簡(jiǎn)單性能測(cè)試
            long start = System.nanoTime();
            for (int i = 0; i < 1000000; i++) Math.sqrt(i);
            long end = System.nanoTime();
            System.out.printf("??  計(jì)算測(cè)試耗時(shí): %.2f ms%n", (end - start) / 1_000_000.0);
            
        } catch (Exception e) {
            System.err.println("? 驗(yàn)證失敗: " + e.getMessage());
            System.exit(1);
        }
    }
}
EOF

# 6. 編譯并運(yùn)行驗(yàn)證
javac /tmp/validate-kernel.java
java -cp /tmp ValidateKernel

if [ $? -eq 0 ]; then
    echo "?? 所有步驟成功完成！請(qǐng)重啟系統(tǒng)生效。"
    echo "?? 建議命令: sudo reboot"
else
    echo "?? 驗(yàn)證失敗，請(qǐng)檢查日志"
fi

# 安裝 perf
sudo apt install linux-tools-common linux-tools-generic

# 監(jiān)控 Java 進(jìn)程的系統(tǒng)調(diào)用
sudo perf stat -e syscalls:sys_enter_* java -jar your-app.jar

# 生成火焰圖分析性能瓶頸
sudo perf record -F 99 -p $(pgrep -f your-app.jar) -g -- sleep 30
sudo perf script | ./FlameGraph/stackcollapse-perf.pl | ./FlameGraph/flamegraph.pl > flame.svg

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import java.lang.management.MemoryMXBean;

public class KernelImpactMonitor {
    private static ThreadMXBean threadBean = ManagementFactory.getThreadMXBean();
    private static MemoryMXBean memoryBean = ManagementFactory.getMemoryMXBean();

    public static void monitor() {
        long prevCpuTime = threadBean.getCurrentThreadCpuTime();
        long prevUserTime = threadBean.getCurrentThreadUserTime();
        
        try { Thread.sleep(1000); } catch (InterruptedException e) {}

        long currCpuTime = threadBean.getCurrentThreadCpuTime();
        long currUserTime = threadBean.getCurrentThreadUserTime();

        System.out.printf("CPU 時(shí)間變化: %d ns%n", currCpuTime - prevCpuTime);
        System.out.printf("用戶態(tài)時(shí)間: %d ns%n", currUserTime - prevUserTime);
        System.out.printf("內(nèi)存使用: %d MB%n", 
            memoryBean.getHeapMemoryUsage().getUsed() / 1024 / 1024);
    }

    public static void main(String[] args) throws InterruptedException {
        System.out.println("?? 開(kāi)始監(jiān)控內(nèi)核對(duì) Java 應(yīng)用的影響...");
        
        for (int i = 0; i < 10; i++) {
            System.out.println("=== 第 " + (i+1) + " 輪監(jiān)控 ===");
            monitor();
            Thread.sleep(2000);
        }
    }
}