SpinPause() should be inlined?

[daniel.daugherty at oracle.com]

Here's the RFE where that was discussed back in 2018:

     JDK-8208458 Simplify and inline os::SpinPause() for non-Windows OS 
on X86
     https://bugs.openjdk.java.net/browse/JDK-8208458

Dan

On 6/22/21 10:51 AM, Yasumasa Suenaga wrote:
> Hi all,
>
> I saw lock contention in SecureRandom. When I was analyzing it, I had 
> a question.
>
> ObjectMonitor::TrySpin() calls SpinPause(). SpinPause() would issue 
> PAUSE, but it is not inlined as following:
>
> ```
>  1587e90:       f0 4d 0f b1 2e          lock cmpxchg %r13,(%r14)
>  1587e95:       48 85 c0                test   %rax,%rax
>  1587e98:       74 16                   je     1587eb0 
> <ObjectMonitor::TrySpin(JavaThread*)+0x60>
>  1587e9a:       e8 31 7b d4 ff          callq  12cf9d0 <SpinPause>
>  1587e9f:       83 eb 01                sub    $0x1,%ebx
>  1587ea2:       72 da                   jb     1587e7e 
> <ObjectMonitor::TrySpin(JavaThread*)+0x2e>
> ```
>
> I found following comment about it in os.hpp. It says SpinPause() 
> should be inlined.
>
> ```
> // Note that "PAUSE" is almost always used with synchronization
> // so arguably we should provide Atomic::SpinPause() instead
> // of the global SpinPause() with C linkage.
> // It'd also be eligible for inlining on many platforms.
> ```
>
> According to Intel Software Developer's Manual, PAUSE seems to need to 
> be inlined, but I'm not sure it can be allow through function call.
> I've fixed it to do so for Linux x64 [1] and I benchmarked with [2], 
> then I saw some advantage in PAUSE on my Core i3-8145U, but it may be 
> within the margin of error.
>
> * original
> Benchmark                       (algo)  (bytes)   Mode  Cnt Score  
>       Error  Units
> RandomBenchmark.fillRandomInMT    DRBG       16  thrpt    3 510141.578 
> ± 138543.261  ops/s
>
> * with inlined PAUSE
> Benchmark                       (algo)  (bytes)   Mode  Cnt Score  
>      Error  Units
> RandomBenchmark.fillRandomInMT    DRBG       16  thrpt    3 531589.958 
> ± 66942.549  ops/s
>
>
> Should be inlined PAUSE as `Atomic::SpinPause()`?
>
>
> Thanks,
>
> Yasumasa
>
>
> [1] 
> https://github.com/YaSuenag/jdk/commit/66b31d35fac6fb0537bb9d85957157342fec564d
> [2] 
> https://github.com/YaSuenag/hwrand/blob/master/benchmark/src/main/java/com/yasuenag/hwrand/benchmark/RandomBenchmark.java#L59-L64