Centos 7，System.nanoTime比Windows慢400倍

Question

我已经看过并阅读了有关为什么System.nanoTime（）在某些操作系统上比其他操作系统更慢的帖子，但是我从来没有看到任何解释我现在看到的差异的东西。 使用JMH，我正在运行此基准测试。 （注意：它也使用System.nanoTime（））

@Benchmark
public long systemNanoTime() {
    return System.nanoTime();
}

在Windows 10上，这需要大约25 ns。

在Centos 7上，Linux 3.10测量为~10293 ns。

这是在同一台机器上，Intel（R）Core（TM）i7-7820X CPU @ 3.60GHz

是否有选项可以改变JDK获取系统时钟的方式？

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编辑：根据托德提供的链接，似乎tsc不可用

# more /sys/devices/system/clocksource/clocksource0/*
::::::::::::::
/sys/devices/system/clocksource/clocksource0/available_clocksource
::::::::::::::
hpet acpi_pm 
::::::::::::::
/sys/devices/system/clocksource/clocksource0/current_clocksource
::::::::::::::
hpet

表演后

echo acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource

延迟有所改善，但仍然很差，延迟为1,816 ns。

我试图找出TSC时钟源是否可以添加到Centos，但还没有运气。

---

编辑：进一步挖掘

# dmesg | grep -i tsc
[    0.000000] tsc: Detected 3600.000 MHz processor
[    0.058602] TSC deadline timer enabled
[    0.065868] TSC synchronization [CPU#0 -> CPU#1]:
[    0.065870] Measured 679995254538 cycles TSC warp between CPUs, turning off TSC clock.
[    0.065874] tsc: Marking TSC unstable due to check_tsc_sync_source failed
[  125.451480] Override clocksource tsc is not HRT compatible. Cannot switch while in HRT/NOHZ mode

Answer 1

基于@ apangin的建议，我在此页面上添加了最新版本的centos备用存储库

http://elrepo.org/tiki/tiki-index.php

然后按照这里的进一步说明进行操作

https://www.tecmint.com/install-upgrade-kernel-version-in-centos-7/

安装并重新启动后

# $ dmesg | grep -i tsc
[    0.001000] tsc: Detected 3600.000 MHz processor
[    0.001000] [Firmware Bug]: TSC ADJUST: CPU0: -2100392876408 force to 0
[    0.046075] TSC deadline timer enabled
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU1: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU2: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU3: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU4: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU5: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU6: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU7: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU8: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU9: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU10: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU11: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU12: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU13: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU14: 0
[    0.001000] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2100392876408 CPU15: 0
[    1.337843] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x6c1bafbc2ab, max_idle_ns: 881591058496 ns
[    2.353636] clocksource: Switched to clocksource tsc

建议内核正在调整固件错误。

再次运行测试，使用System.nanoTime（）得到平均延迟为40 ns，这是一个260倍的改进。 这也意味着使用此度量的基准更有意义。