RFR: JDK-8236604: Optimize SystemDictionary::resolve_well_known_classes for CDS

[Claes Redestad]

Hi,

before diving into a full review, I took your patch for a spin and
can confirm a speed-up around .5ms, along with about a 1% reduction of
#instructions and #branches on Hello World[1]. Sweet!

/Claes

[1]
Baseline:
          53.028269      task-clock (msec)         #    1.396 CPUs 
utilized            ( +-  0.34% )
                244      context-switches          #    0.005 M/sec 
               ( +-  0.60% )
                 32      cpu-migrations            #    0.607 K/sec 
               ( +-  0.39% )
              3,634      page-faults               #    0.069 M/sec 
               ( +-  0.03% )
        138,590,680      cycles                    #    2.614 GHz 
               ( +-  0.25% )
        112,946,802      instructions              #    0.81  insns per 
cycle          ( +-  0.06% )
         22,428,330      branches                  #  422.950 M/sec 
               ( +-  0.06% )
            771,755      branch-misses             #    3.44% of all 
branches          ( +-  0.13% )

        0.037981200 seconds time elapsed 
          ( +-  0.39% )

Patched:
          52.537826      task-clock (msec)         #    1.409 CPUs 
utilized            ( +-  0.26% )
                244      context-switches          #    0.005 M/sec 
               ( +-  0.65% )
                 32      cpu-migrations            #    0.607 K/sec 
               ( +-  0.43% )
              3,637      page-faults               #    0.069 M/sec 
               ( +-  0.04% )
        137,129,495      cycles                    #    2.610 GHz 
               ( +-  0.23% )
        111,931,764      instructions              #    0.82  insns per 
cycle          ( +-  0.07% )
         22,215,346      branches                  #  422.845 M/sec 
               ( +-  0.07% )
            766,573      branch-misses             #    3.45% of all 
branches          ( +-  0.13% )

        0.037283845 seconds time elapsed 
          ( +-  0.30% )


On 2020-02-25 06:02, Yumin Qi wrote:
> Hi,
> 
>     Please review fix:
> 
>     Bug: https://bugs.openjdk.java.net/browse/JDK-8236604
> 
>     Webrev:http://cr.openjdk.java.net/~minqi/8236604/webrev-00
> 
>      Description: Optimize well known classes initialization for CDS 
> during jvm startup.
> 
>      When run with CDS, initialize well known classes (95 classes) will 
> call resolve_or_fail thus go though the resolve functions, locks etc. 
> The initialization of well-known classes happens in fact in very early 
> stage, those lock can be avoided. The fix is serializing 
> SystemDictionay::_well_known_klasses into CDS  and in runtime restore 
> them by avoiding call resolve_or_fail. Since Compile_lock has to be held 
> for SystemDictionary::add_to_hierachy, the fix avoids calling it by 
> copying the code from it in SytemDictionary::quick_resolve, but this way 
> I have to remove two asserts which will assert on Compile_lock. The 
> reminding usage of the lock was added as comments on the function 
> declarations of Klass::append_to_sibling_list and 
> InstanceKlass::add_implementor. The two functions calling paths have 
> been checked to make sure they are not used in other places.
> 
>       Performance measured by take time before and after 
> SystemDictionary::resolve_well_known_classes(manually modified 
> orignal/new versions), since this is the most direct measurement and 
> accurate(excluded in review code):
> 
>      + jlong s0 = os::javaTimeNanos();
>       resolve_well_known_classes(CHECK);
> 
>       + jlong s1 = os::javaTimeNanos();
> 
>       // print out s1 - s0
> 
>       Run -version 2000 times for original/new versions respectively and 
> took the averages. The saving is about 18% (2.9ms vs 2.4ms), it is not a 
> big saving but still helps to improve the startup time.
> 
>      Testing: local jtreg test on linux-x86.
> 
>      pending mach5 hs-tier1-4
> 
> 
> Thanks
> 
> Yumin
>