在较新的 JVM 上,在 for 循环中对数组中的所有元素求和的性能(吞吐量)比 Java 1.8.0 JDK 中的 JVM 慢。我执行了 JHM 基准测试(下图)。在每次测试之前,源代码由提供的 javac.exe 编译并由 java.exe 运行,这两个二进制文件都由选定的 JDK 提供。测试是在 Windows 10 上执行的,并由 powershell 脚本启动,没有在后台运行任何程序(没有其他 jvm)。计算机配备了 32GB 的 RAM,因此未使用 HDD 上的虚拟内存。
数组中的 10M 个元素:
数组中的 100M 个元素:
我的测试源代码:
@Param({"10000000", "100000000"})
public static int ELEMENTS;
public static void main(String[] args) throws RunnerException, IOException {
File outputFile = new File(args[0]);
int javaMajorVersion = Integer.parseInt(System.getProperty("java.version").split("\\.")[0]);
ChainedOptionsBuilder builder = new OptionsBuilder()
.include(IteratingBenchmark.class.getSimpleName())
.mode(Mode.Throughput)
.forks(2)
.measurementTime(TimeValue.seconds(10))
.measurementIterations(50)
.warmupTime(TimeValue.seconds(2))
.warmupIterations(10)
.resultFormat(ResultFormatType.SCSV)
.result(outputFile.getAbsolutePath());
if (javaMajorVersion > 8) {
builder = builder.jvmArgs("-Xms20g", "-Xmx20g", "--enable-preview");
} else {
builder = builder.jvmArgs("-Xms20g", "-Xmx20g");
}
new Runner(builder.build()).run();
}
@Benchmark
public static void cStyleForLoop(Blackhole bh, MockData data) {
long sum = 0;
for (int i = 0; i < data.randomInts.length; i++) {
sum += data.randomInts[i];
}
bh.consume(sum);
}
@State(Scope.Thread)
public static class MockData {
private int[] randomInts = new int[ELEMENTS];
@Setup(Level.Iteration)
public void setup() {
Random r = new Random();
this.randomInts = Stream.iterate(r.nextInt(), i -> i + r.nextInt(1022) + 1).mapToInt(Integer::intValue).limit(ELEMENTS).toArray();
}
}
原始数据:JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;331,446104;5,563589;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;33,757268;0,431403;"ops/s";100000000
JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,728461;4,823611;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,075948;0,062830;"ops/s";100000000
JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,914782;4,450969;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,095232;0,075051;"ops/s";100000000
JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;325,103055;4,933257;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,228403;0,067954;"ops/s";100000000
JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,861148;0,443404;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,863602;0,035781;"ops/s";100000000
OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,781930;0,481579;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,873509;0,033055;"ops/s";100000000
OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;343,530895;0,445551;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;34,287083;0,035028;"ops/s";100000000
是否有任何有效的解释,为什么较新版本的 Java 比 1.8 慢(OpenJDK 15 除外)?更新 1:
我对不同的 Xmx/Xms 值运行相同的测试(对于每个测试 Xmx == Xms),结果如下:
更新 2:
Level.Iteration
至 Level.Trial
. 结果:
原始数据:
JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;33,760346;0,089646;"ops/s";100000000
JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,075120;0,086171;"ops/s";100000000
JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,173939;0,044176;"ops/s";100000000
JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,219283;0,062329;"ops/s";100000000
JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,808609;0,072664;"ops/s";100000000
OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,845817;0,074315;"ops/s";100000000
OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;34,310620;0,087412;"ops/s";100000000
更新 3:我做了 GitHub Repository包含基准源代码,以及使用我使用的 JMH 参数执行基准测试的脚本,它会自动生成 png 格式的图。
此外,我在其他机器(Linux)上执行了基准测试。 Linux机器的结果似乎更乐观:
不幸的是,在我的 Windows 机器上,结果仍然显示性能下降(不包括 JDK 15)。
更新 4:
结果与
-XX:-UseCountedLoopSafepoints
:最佳答案
即使在从 GitHub 逐字复制您的基准测试之后并使用相同的参数运行,我仍然无法重现结果。在我的环境中,JDK 14 的执行速度与 JDK 8 一样快(甚至快一点)。因此,在这个答案中,我将根据编译代码的反汇编来分析两个版本之间的差异。
首先,让我们采用来自同一供应商的最新 OpenJDK 版本。
我这里比较Liberica JDK 8u265+1和 Liberica JDK 14.0.2+13对于 Windows 64 位。
JMH分数如下:
Benchmark (ELEMENTS) Mode Cnt Score Error Units
IteratingBenchmark.cStyleForLoop 10000000 thrpt 30 263,137 ± 0,484 ops/s # JDK 8
IteratingBenchmark.cStyleForLoop 10000000 thrpt 30 264,406 ± 0,788 ops/s # JDK 14
现在让我们运行内置的 JMH -prof xperfasm
profiler 查看对基准测试 HitTest 部分的反汇编。预计大约 99.5% 的 CPU 时间花费在 C2 编译 cStyleForLoop
方法。JDK 8 上 HitTest 的区域
....[Hottest Region 1]..............................................................................
C2, level 4, codes.dbg.IteratingBenchmark::cStyleForLoop, version 574 (71 bytes)
0x0000028c5607fc5f: add r10d,0fffffff9h
0x0000028c5607fc63: lea rax,[r12+rcx*8]
0x0000028c5607fc67: mov ebx,80000000h
0x0000028c5607fc6c: cmp r9d,r10d
0x0000028c5607fc6f: cmovl r10d,ebx
0x0000028c5607fc73: mov r9d,1h
0x0000028c5607fc79: cmp r10d,1h
╭ 0x0000028c5607fc7d: jle 28c5607fccch
│ 0x0000028c5607fc7f: nop ;*lload_2
│ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25)
0,07% │↗ 0x0000028c5607fc80: movsxd rbx,dword ptr [rax+r9*4+10h]
0,06% ││ 0x0000028c5607fc85: add rbx,r8
8,93% ││ 0x0000028c5607fc88: movsxd rcx,r9d
0,41% ││ 0x0000028c5607fc8b: movsxd r8,dword ptr [rax+rcx*4+2ch]
25,02% ││ 0x0000028c5607fc90: movsxd rdi,dword ptr [rax+rcx*4+14h]
0,10% ││ 0x0000028c5607fc95: movsxd rsi,dword ptr [rax+rcx*4+18h]
8,56% ││ 0x0000028c5607fc9a: movsxd rbp,dword ptr [rax+rcx*4+28h]
0,58% ││ 0x0000028c5607fc9f: movsxd r13,dword ptr [rax+rcx*4+1ch]
0,41% ││ 0x0000028c5607fca4: movsxd r14,dword ptr [rax+rcx*4+20h]
0,20% ││ 0x0000028c5607fca9: movsxd rcx,dword ptr [rax+rcx*4+24h]
8,85% ││ 0x0000028c5607fcae: add rdi,rbx
0,38% ││ 0x0000028c5607fcb1: add rsi,rdi
0,15% ││ 0x0000028c5607fcb4: add r13,rsi
8,57% ││ 0x0000028c5607fcb7: add r14,r13
13,76% ││ 0x0000028c5607fcba: add rcx,r14
5,51% ││ 0x0000028c5607fcbd: add rbp,rcx
8,50% ││ 0x0000028c5607fcc0: add r8,rbp ;*ladd
││ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25)
8,95% ││ 0x0000028c5607fcc3: add r9d,8h ;*iinc
││ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@26 (line 24)
0,40% ││ 0x0000028c5607fcc7: cmp r9d,r10d
│╰ 0x0000028c5607fcca: jl 28c5607fc80h ;*if_icmpge
│ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@12 (line 24)
↘ 0x0000028c5607fccc: cmp r9d,edx
0x0000028c5607fccf: jnl 28c5607fce4h
0x0000028c5607fcd1: nop ;*lload_2
; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25)
0x0000028c5607fcd4: movsxd r10,dword ptr [rax+r9*4+10h]
0x0000028c5607fcd9: add r8,r10 ;*ladd
; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25)
....................................................................................................
JDK 14 上 HitTest 的区域 ....[Hottest Region 1]..............................................................................
c2, level 4, codes.dbg.IteratingBenchmark::cStyleForLoop, version 622 (147 bytes)
; - codes.dbg.IteratingBenchmark::cStyleForLoop@23 (line 25)
0x000001e844438f72: mov r11d,r10d
0x000001e844438f75: add r11d,0fffffff9h
0x000001e844438f79: lea rax,[r12+r9*8]
0x000001e844438f7d: mov ebx,1h
0x000001e844438f82: cmp r11d,1h
0x000001e844438f86: jle 1e8444390c0h ;*goto {reexecute=0 rethrow=0 return_oop=0}
; - codes.dbg.IteratingBenchmark::cStyleForLoop@29 (line 24)
╭ 0x000001e844438f8c: jmp 1e844438ffah
│ 0x000001e844438f8e: nop
0,04% │↗ 0x000001e844438f90: mov rsi,r8 ;*lload_2 {reexecute=0 rethrow=0 return_oop=0}
││ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25)
0,04% ││ ↗ 0x000001e844438f93: movsxd rdx,dword ptr [rax+rbx*4+10h]
8,41% ││ │ 0x000001e844438f98: movsxd rbp,dword ptr [rax+rbx*4+14h]
1,23% ││ │ 0x000001e844438f9d: movsxd r13,dword ptr [rax+rbx*4+18h]
0,03% ││ │ 0x000001e844438fa2: movsxd r8,dword ptr [rax+rbx*4+2ch]
23,87% ││ │ 0x000001e844438fa7: movsxd r11,dword ptr [rax+rbx*4+28h]
8,22% ││ │ 0x000001e844438fac: movsxd r9,dword ptr [rax+rbx*4+24h]
1,25% ││ │ 0x000001e844438fb1: movsxd rcx,dword ptr [rax+rbx*4+20h]
0,14% ││ │ 0x000001e844438fb6: movsxd r14,dword ptr [rax+rbx*4+1ch]
0,28% ││ │ 0x000001e844438fbb: add rdx,rsi
7,82% ││ │ 0x000001e844438fbe: add rbp,rdx
1,14% ││ │ 0x000001e844438fc1: add r13,rbp
0,17% ││ │ 0x000001e844438fc4: add r14,r13
14,57% ││ │ 0x000001e844438fc7: add rcx,r14
11,05% ││ │ 0x000001e844438fca: add r9,rcx
5,26% ││ │ 0x000001e844438fcd: add r11,r9
6,32% ││ │ 0x000001e844438fd0: add r8,r11 ;*ladd {reexecute=0 rethrow=0 return_oop=0}
││ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25)
8,45% ││ │ 0x000001e844438fd3: add ebx,8h ;*iinc {reexecute=0 rethrow=0 return_oop=0}
││ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@26 (line 24)
1,15% ││ │ 0x000001e844438fd6: cmp ebx,edi
│╰ │ 0x000001e844438fd8: jl 1e844438f90h ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
│ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@12 (line 24)
│ │ 0x000001e844438fda: mov r11,qword ptr [r15+110h] ; ImmutableOopMap {rax=Oop xmm0=Oop xmm1=Oop }
│ │ ;*goto {reexecute=1 rethrow=0 return_oop=0}
│ │ ; - (reexecute) codes.dbg.IteratingBenchmark::cStyleForLoop@29 (line 24)
0,00% │ │ 0x000001e844438fe1: test dword ptr [r11],eax ;*goto {reexecute=0 rethrow=0 return_oop=0}
│ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@29 (line 24)
│ │ ; {poll}
0,02% │ │ 0x000001e844438fe4: cmp ebx,dword ptr [rsp]
│ ╭│ 0x000001e844438fe7: jnl 1e844439028h
0,00% │ ││ 0x000001e844438fe9: mov rsi,r8
│ ││ 0x000001e844438fec: vmovq r8,xmm0
│ ││ 0x000001e844438ff1: vmovq rdx,xmm1
0,01% │ ││ 0x000001e844438ff6: mov r11d,dword ptr [rsp]
↘ ││ 0x000001e844438ffa: mov ecx,r10d
││ 0x000001e844438ffd: sub ecx,ebx
││ 0x000001e844438fff: add ecx,0fffffff9h
0,00% ││ 0x000001e844439002: mov r9d,1f40h
││ 0x000001e844439008: cmp r9d,ecx
││ 0x000001e84443900b: mov edi,1f40h
││ 0x000001e844439010: cmovnle edi,ecx
0,02% ││ 0x000001e844439013: add edi,ebx
││ 0x000001e844439015: vmovq xmm0,r8
││ 0x000001e84443901a: vmovq xmm1,rdx
││ 0x000001e84443901f: mov dword ptr [rsp],r11d
0,01% │╰ 0x000001e844439023: jmp 1e844438f93h
↘ 0x000001e844439028: vmovq rdx,xmm1
0x000001e84443902d: cmp ebx,r10d
0x000001e844439030: jnl 1e844439043h
0x000001e844439032: nop ;*lload_2 {reexecute=0 rethrow=0 return_oop=0}
; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25)
0x000001e844439034: movsxd r11,dword ptr [rax+rbx*4+10h]
0x000001e844439039: add r8,r11 ;*ladd {reexecute=0 rethrow=0 return_oop=0}
; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25)
0x000001e84443903c: inc ebx ;*iinc {reexecute=0 rethrow=0 return_oop=0}
; - codes.dbg.IteratingBenchmark::cStyleForLoop@26 (line 24)
....................................................................................................
正如我们所见,循环体在两个 JDK 上的编译方式相似:add
指示; 关键区别在于,在 JDK 14 上,循环迭代被拆分为两个嵌套块。这是 Loop strip mining 的结果JDK 10 中出现了优化。这种优化的想法是将计数循环拆分为没有安全点轮询的热内部部分和具有安全点轮询指令的外部部分。
C2 JIT 将循环转换为类似
for (int i = 0; i < array.length; i += 8000) {
for (int j = 0; j < 8000; j += 8) {
int ix = i + j;
int v0 = array[ix];
int v1 = array[ix + 1];
...
int v7 = array[ix + 7];
sum += v0 + v1 + ... + v7;
}
safepoint_poll();
}
请注意,JDK 8 版本在计数循环内根本没有安全点轮询。一方面,这可以使循环运行得更快。但另一方面,这对于低延迟应用程序来说实际上是不利的,因为暂停时间可能会随着整个循环的持续时间而增加。JDK 14 在循环中插入安全点轮询。这可能是您观察到速度变慢的原因,但我并不相信这一点,因为由于循环带挖掘优化,安全点轮询在 8000 次迭代中仅执行一次。
要验证这一点,您可以使用
-XX:-UseCountedLoopSafepoints
禁用安全点轮询。 JVM 选项。在这种情况下,JDK 14 编译版本看起来与 JDK 8 几乎相同。基准分数也是如此。
关于java - 降低新 JVM 的性能,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/63524800/