On 02/04/2018 12:31 AM, John Hening wrote:
> |
> publicstaticintdontOptimize;
>
>
> publicstaticintsimple(){
> returndontOptimize;
> }
> |
>
> And JITed version of that:
> 0x00007fdc75112aa0:mov %eax,-0x14000(%rsp)
> 0x00007fdc75112aa7:push %rbp
> 0x00007fdc75112aa8:sub $0x30,%rsp
> *_0x00007fdc75112aac_*:mov $0x7fdc7443be90,%rax ; {metadata(method data
> for{method}{0x00007fdc7443bb30}'simple''()I'in'Main')}
> 0x00007fdc75112ab6:mov 0xdc(%rax),%esi
>
> Though I know understand I cannot understand a such simple code. Especially,
> what does lines between
> |0x00007fdc75112aac-|||_*0x00007fdc75112ad8*_| means? I highlighted it.
This is most likely the method compiled at level 2/3 (C1 with profiling), and
the updates you see at
...aac are updates of profiling data. It is unlikely to be on hotpath -- if it
is, this is the
performnace bug in tiered compilation machinery.
Zen question: How do you know you got the the version you have executed on hot
path? With tiered
compilation, on-stack replacement, deoptimization, etc. there are much more
than 1 version of the
method, JMH's -prof perfasm can be used to highlight what version is actually
executing. For example:
public static int dontOptimize;
@Benchmark
@CompilerControl(CompilerControl.Mode.DONT_INLINE)
public int test() {
return dontOptimize;
}
Yields:
C1, level 1, org.openjdk.StaticBench::test, version 443 (36 bytes)
...
[Verified Entry Point]
3.16% 0x00007f63c91b0e80: mov %eax,-0x14000(%rsp)
3.35% 0x00007f63c91b0e87: push %rbp
1.65% 0x00007f63c91b0e88: sub $0x30,%rsp
2.39% 0x00007f63c91b0e8c: movabs $0x782737b50,%rax ; {oop(a
'java/lang/Class'
=
'org/openjdk/StaticBench')}
2.86% 0x00007f63c91b0e96: mov 0x68(%rax),%eax ;*getstatic dontOptimize
; -
org.openjdk.StaticBench::test@0 (line 44)
1.75% 0x00007f63c91b0e99: add $0x30,%rsp
1.26% 0x00007f63c91b0e9d: pop %rbp
0.82% 0x00007f63c91b0e9e: test %eax,0x1774025c(%rip) #
0x00007f63e08f1100
; {poll_return}
3.14% 0x00007f63c91b0ea4: retq
The method is trivial, and so compilation stops at level 1.
-XX:-TieredComplation yields:
C2, org.openjdk.StaticBench::test, version 82 (37 bytes)
...
[Verified Entry Point]
7.11% 0x00007fbdb109c6c0: sub $0x18,%rsp
0.18% 0x00007fbdb109c6c7: mov %rbp,0x10(%rsp) ;*synchronization entry
;
org.openjdk.StaticBench::test@-1 (line 44)
0.04% 0x00007fbdb109c6cc: movabs $0x782647980,%r10 ; {oop(a
'java/lang/Class' =
'org/openjdk/StaticBench')}
6.25% 0x00007fbdb109c6d6: mov 0x68(%r10),%eax ;*getstatic dontOptimize
; -
org.openjdk.StaticBench::test@0 (line 44)
0x00007fbdb109c6da: add $0x10,%rsp
0.08% 0x00007fbdb109c6de: pop %rbp
27.58% 0x00007fbdb109c6df: test %eax,0xccef91b(%rip) # 0x00007fbdbdd8c000
; {poll_return}
0.02% 0x00007fbdb109c6e5: retq
...which is almost the same code, and this is why tiered compilation policy is
happy with Level 1
compilation.
-Aleksey
--
You received this message because you are subscribed to the Google Groups
"mechanical-sympathy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to mechanical-sympathy+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
signature.asc
Description: OpenPGP digital signature
