当我有一些紧密交互的线程时,它可以减少延迟并增加吞吐量。对于单线程任务,它仍然可以大幅减少抖动。
这个程序查看System.nanoTime()
调用之间的时间差,并报告超过10x,000 ns的差异。
public class TimeJumpingMain {
static final long IGNORE_TIME = 1000 * 1000 * 1000; // the first second to allow warmup.
static final int minJump = 10; // smallest jump of 10 us.
static final int midJump = 100; // mid size jump of 100 us.
static final int bigJump = 1000; // big jump of 1 ms.
public static void main(String... args) {
int[] intervalTimings = new int[1000];
int[] jumpTimings = new int[1000];
long start = System.nanoTime();
long prev = start;
long prevJump = start;
int jumpCount = 0;
int midJumpCount = 0;
int bigJumpCount = 0;
while (true) {
long now = System.nanoTime();
long jump = (now - prev) / 1000;
if (jump > minJump && now - start > IGNORE_TIME) {
long interval = (now - prevJump) / 1000;
if (jumpCount < intervalTimings.length) {
intervalTimings[jumpCount] = (int) interval;
jumpTimings[jumpCount] = (int) jump;
}
if (jump >= midJump)
midJumpCount++;
if (jump >= bigJump)
bigJumpCount++;
prevJump = now;
jumpCount++;
}
prev = now;
if (now - start > 120L * 1000 * 1000 * 1000 + IGNORE_TIME)
break;
}
System.out.println("interval us\tdelay us");
for (int i = 0; i < jumpCount && i < intervalTimings.length; i++) {
System.out.println(intervalTimings[i] + "\t" + jumpTimings[i]);
}
System.out.printf("Time jumped %,d / %,d / %,d times by at least %,d / %,d / %,d us in %.1f seconds %n",
jumpCount, midJumpCount, bigJumpCount, minJump, midJump, bigJump, (System.nanoTime() - start - IGNORE_TIME) / 1e9);
}
}
在我的机器上,这报告如下。
Time jumped 2,905 / 131 / 20 times by at least 10 / 100 / 1,000 us in 120.0 seconds
我曾尝试使用
chrt
来设置实时优先级,以及使用taskset
在启动进程后尝试锁定到单个核心,但这些并没有像我预期的那样有所帮助。我将所有中断移动到了CPU 0-3,并将所有进程的CPU掩码从0xFF更改为0x0F。在
top
中,前四个CPU大约99%空闲,而最后四个CPU则是100.0%空闲。作为root用户,使用
chrt -r 99
。Time jumped 673 / 378 / 44 times by at least 10 / 100 / 1,000 us in 120.0 seconds
然而,当单独使用 taskset -c 7
时(我已确保cpu7空闲)
Time jumped 24 / 1 / 0 times by at least 10 / 100 / 1,000 us in 120.0 seconds
使用 chrt - r 99 taskset -c 7
命令
Time jumped 7 / 1 / 0 times by at least 10 / 100 / 1,000 us in 120.0 seconds
看起来在进程启动后尝试使用taskset并不起作用。
更广泛的问题是:
如何减少Java进程的抖动?还有没有其他减少Linux上抖动的技巧?
注意:此进程运行期间不会发生GC(使用-verbosegc进行了检查)
似乎代码编译可能会导致每次延迟3.62毫秒,每100-102毫秒一次。因此,我忽略第一秒钟中的所有内容作为预热。